diff --git a/packages/cli/src/commands/check.test.ts b/packages/cli/src/commands/check.test.ts
index 8d9a07f97e..2a9c6f77b1 100644
--- a/packages/cli/src/commands/check.test.ts
+++ b/packages/cli/src/commands/check.test.ts
@@ -934,6 +934,91 @@ describe("check pipeline", () => {
     expect(browser).toHaveBeenCalledTimes(1);
   });
 
+  // An ambiguous selector used to zero the sample grid, so every other assertion in the sidecar
+  // went unevaluated with no trace — the section still reported `enabled`.
+  it("keeps evaluating the unambiguous assertions when one selector is ambiguous", async () => {
+    const motion: MotionSpecResolution = {
+      kind: "valid",
+      path: "/project/index.motion.json",
+      spec: {
+        assertions: [
+          { kind: "appearsBy", selector: ".item", bySec: 1 },
+          { kind: "appearsBy", selector: "#hero", bySec: 0.2 },
+        ],
+      },
+    };
+    const driver = fakeDriver({
+      getDuration: vi.fn(async () => 1),
+      findAmbiguousSelectors: vi.fn(async () => [
+        { ...layoutIssue("error", { code: "motion_selector_ambiguous" }), selector: ".item" },
+      ]),
+      collectMotionFrame: vi.fn(async (time: number) => heroMotionFrame(time, (t) => t >= 0.5)),
+    });
+    const { report } = await runScenario(driver, {}, { motion });
+
+    expect(report.motion.samples).toBeGreaterThan(0);
+    expect(report.motion.findings.map((finding) => finding.code).sort()).toEqual([
+      "motion_appears_late",
+      "motion_selector_ambiguous",
+    ]);
+    expect(report.ok).toBe(false);
+    // The grid is sampled again, so the report must say on its own that part of the spec was dropped.
+    expect(
+      report.motion.findings.find((finding) => finding.code === "motion_selector_ambiguous")
+        ?.message,
+    ).toContain("1 assertion(s) naming it were not evaluated");
+    // Only the surviving assertion's selector is sampled.
+    expect(driver.collectMotionFrame).toHaveBeenCalledWith(expect.any(Number), ["#hero"], []);
+  });
+
+  it("drops a before assertion when either side is ambiguous, keeping the rest", async () => {
+    const motion: MotionSpecResolution = {
+      kind: "valid",
+      path: "/project/index.motion.json",
+      spec: {
+        assertions: [
+          { kind: "before", a: "#hero", b: ".item" },
+          { kind: "appearsBy", selector: "#hero", bySec: 0.2 },
+        ],
+      },
+    };
+    const driver = fakeDriver({
+      getDuration: vi.fn(async () => 1),
+      findAmbiguousSelectors: vi.fn(async () => [
+        { ...layoutIssue("error", { code: "motion_selector_ambiguous" }), selector: ".item" },
+      ]),
+      collectMotionFrame: vi.fn(async (time: number) => heroMotionFrame(time, (t) => t >= 0.5)),
+    });
+    const { report } = await runScenario(driver, {}, { motion });
+
+    expect(report.motion.findings.map((finding) => finding.code).sort()).toEqual([
+      "motion_appears_late",
+      "motion_selector_ambiguous",
+    ]);
+    // `#hero` survives via the appearsBy assertion even though the before naming it was dropped.
+    expect(driver.collectMotionFrame).toHaveBeenCalledWith(expect.any(Number), ["#hero"], []);
+  });
+
+  it("does not sample when every assertion names an ambiguous selector", async () => {
+    const motion: MotionSpecResolution = {
+      kind: "valid",
+      path: "/project/index.motion.json",
+      spec: { assertions: [{ kind: "appearsBy", selector: ".item", bySec: 1 }] },
+    };
+    const driver = fakeDriver({
+      getDuration: vi.fn(async () => 1),
+      findAmbiguousSelectors: vi.fn(async () => [
+        { ...layoutIssue("error", { code: "motion_selector_ambiguous" }), selector: ".item" },
+      ]),
+    });
+    const { report } = await runScenario(driver, {}, { motion });
+
+    expect(report.motion.samples).toBe(0);
+    expect(report.motion.findings.map((finding) => finding.code)).toEqual([
+      "motion_selector_ambiguous",
+    ]);
+  });
+
   it("reports a failing appearsBy sidecar as motion_appears_late", async () => {
     const motion: MotionSpecResolution = {
       kind: "valid",
diff --git a/packages/cli/src/utils/checkPipeline.ts b/packages/cli/src/utils/checkPipeline.ts
index a02fb2fa5b..80a7bd6f04 100644
--- a/packages/cli/src/utils/checkPipeline.ts
+++ b/packages/cli/src/utils/checkPipeline.ts
@@ -15,12 +15,13 @@ import {
   type LayoutRect,
 } from "./layoutAudit.js";
 import {
+  assertionTargets,
   collectSamplingTargets,
   evaluateMotion,
   type Canvas,
   type MotionFrame,
 } from "./motionAudit.js";
-import { findMotionSpec, readMotionSpec } from "./motionSpec.js";
+import { findMotionSpec, readMotionSpec, type MotionAssertion } from "./motionSpec.js";
 import { normalizeErrorMessage } from "./errorMessage.js";
 import {
   parseColorRGBA,
@@ -167,6 +168,8 @@ interface MotionPlan {
   selectors: string[];
   livenessScopes: string[];
   preflightIssues: AnchoredLayoutIssue[];
+  /** Assertions naming no ambiguous selector; a zero-match selector survives and reports as missing. */
+  assertions: MotionAssertion[];
 }
 
 async function planMotionSampling(
@@ -175,13 +178,30 @@ async function planMotionSampling(
   duration: number,
 ): Promise<MotionPlan> {
   if (motion.kind !== "valid") {
-    return { times: [], selectors: [], livenessScopes: [], preflightIssues: [] };
+    return { times: [], selectors: [], livenessScopes: [], preflightIssues: [], assertions: [] };
   }
-  const targets = collectSamplingTargets(motion.spec.assertions);
-  const preflightIssues = await driver.findAmbiguousSelectors(targets.selectors);
+  const preflightIssues = await driver.findAmbiguousSelectors(
+    collectSamplingTargets(motion.spec.assertions).selectors,
+  );
+  // One ambiguous selector used to zero the grid, so every other assertion went unevaluated in
+  // silence. Drop only the assertions that name it; the rest still run.
+  const ambiguous = new Set(preflightIssues.map((issue) => issue.selector));
+  const assertions = motion.spec.assertions.filter(
+    (assertion) =>
+      !assertionTargets(assertion).selectors.some((selector) => ambiguous.has(selector)),
+  );
+  noteSkippedAssertions(preflightIssues, motion.spec.assertions.length - assertions.length);
+  const targets = collectSamplingTargets(assertions);
   const times =
-    preflightIssues.length === 0 ? buildMotionSampleTimes(motion.spec.duration ?? duration) : [];
-  return { times, ...targets, preflightIssues };
+    assertions.length > 0 ? buildMotionSampleTimes(motion.spec.duration ?? duration) : [];
+  return { times, ...targets, preflightIssues, assertions };
+}
+
+/** Filtering a spec down must not be silent: a sampled grid no longer says on its own that part of the spec went unevaluated. */
+function noteSkippedAssertions(issues: AnchoredLayoutIssue[], skipped: number): void {
+  if (skipped <= 0) return;
+  const suffix = ` ${skipped} assertion(s) naming it were not evaluated.`;
+  for (const issue of issues) issue.message += suffix;
 }
 
 interface GridSamples {
@@ -1000,13 +1020,13 @@ export async function runAuditGrid(
   const seekLoopMs = Date.now() - seekLoopStart;
 
   let motionIssues = plan.preflightIssues;
-  if (motion.kind === "valid" && motionIssues.length === 0 && collected.motionFrames.length > 0) {
+  if (motion.kind === "valid" && plan.assertions.length > 0 && collected.motionFrames.length > 0) {
     const evaluated = evaluateMotion(
       collected.motionFrames,
-      motion.spec.assertions,
+      plan.assertions,
       await driver.getCanvas(),
     );
-    motionIssues = await driver.anchorMotionIssues(evaluated);
+    motionIssues = [...motionIssues, ...(await driver.anchorMotionIssues(evaluated))];
   }
   const sweepFindings = detectSweepStatic(
     grid.duration,
diff --git a/packages/cli/src/utils/motionAudit.ts b/packages/cli/src/utils/motionAudit.ts
index 368de902ee..03d6d09ae0 100644
--- a/packages/cli/src/utils/motionAudit.ts
+++ b/packages/cli/src/utils/motionAudit.ts
@@ -240,6 +240,32 @@ export function evaluateMotion(
  * Selectors and liveness scopes the in-page sampler must read for a spec.
  * Selectors feed the per-element matrix; scopes feed keepsMoving liveness.
  */
+/**
+ * What one assertion resolves against: `selectors` are preflighted for ambiguity
+ * and sampled per element, `scopes` drive liveness. Exhaustive by design — a new
+ * assertion kind must declare its targets here or fail to compile, because a
+ * kind missing from this map would have its ambiguous selector reported AND
+ * still evaluated against an arbitrary first match.
+ */
+export function assertionTargets(assertion: MotionAssertion): {
+  selectors: string[];
+  scopes: string[];
+} {
+  switch (assertion.kind) {
+    case "appearsBy":
+    case "staysInFrame":
+      return { selectors: [assertion.selector], scopes: [] };
+    case "before":
+      return { selectors: [assertion.a, assertion.b], scopes: [] };
+    case "keepsMoving":
+      return { selectors: [], scopes: [assertion.withinSelector ?? "*"] };
+    default: {
+      const exhaustive: never = assertion;
+      return exhaustive;
+    }
+  }
+}
+
 export function collectSamplingTargets(assertions: MotionAssertion[]): {
   selectors: string[];
   livenessScopes: string[];
@@ -247,19 +273,9 @@ export function collectSamplingTargets(assertions: MotionAssertion[]): {
   const selectors = new Set<string>();
   const scopes = new Set<string>();
   for (const assertion of assertions) {
-    switch (assertion.kind) {
-      case "appearsBy":
-      case "staysInFrame":
-        selectors.add(assertion.selector);
-        break;
-      case "before":
-        selectors.add(assertion.a);
-        selectors.add(assertion.b);
-        break;
-      case "keepsMoving":
-        scopes.add(assertion.withinSelector ?? "*");
-        break;
-    }
+    const targets = assertionTargets(assertion);
+    for (const selector of targets.selectors) selectors.add(selector);
+    for (const scope of targets.scopes) scopes.add(scope);
   }
   return { selectors: [...selectors], livenessScopes: [...scopes] };
 }