diff --git a/src/scroll-timeline-base.js b/src/scroll-timeline-base.js
index 6bfc51d..698effe 100644
--- a/src/scroll-timeline-base.js
+++ b/src/scroll-timeline-base.js
@@ -233,9 +233,8 @@ function updateMeasurements(source) {
   if (details.updateScheduled)
     return;
 
-  requestAnimationFrame(() => {
-    // Defer ticking timeline to animation frame to prevent
-    // "ResizeObserver loop completed with undelivered notifications"
+  setTimeout(() => {
+    // Schedule a task to update timelines after all measurements are completed
     for (const ref of details.timelineRefs) {
       const timeline = ref.deref();
       if (timeline) {
@@ -249,7 +248,8 @@ function updateMeasurements(source) {
 }
 
 function updateSource(timeline, source) {
-  const oldSource = scrollTimelineOptions.get(timeline).source;
+  const timelineDetails = scrollTimelineOptions.get(timeline);
+  const oldSource = timelineDetails.source;
   if (oldSource == source)
     return;
 
@@ -273,7 +273,7 @@ function updateSource(timeline, source) {
       }
     }
   }
-  scrollTimelineOptions.get(timeline).source = source;
+  timelineDetails.source = source;
   if (source) {
     let details = sourceDetails.get(source);
     if (!details) {
@@ -288,10 +288,13 @@ function updateSource(timeline, source) {
       // Use resize observer to detect changes to source size
       const resizeObserver = new ResizeObserver((entries) => {
         for (const entry of entries) {
-          updateMeasurements(entry.target)
+          updateMeasurements(timelineDetails.source)
         }
       });
       resizeObserver.observe(source);
+      for (const child of source.children) {
+        resizeObserver.observe(child)
+      }
 
       // Use mutation observer to detect updated style attributes on source element
       const mutationObserver = new MutationObserver((records) => {
diff --git a/test/expected.txt b/test/expected.txt
index 278ef4a..17bdc65 100644
--- a/test/expected.txt
+++ b/test/expected.txt
@@ -676,7 +676,7 @@ PASS	/scroll-animations/scroll-timelines/cancel-animation.html	The finished prom
 PASS	/scroll-animations/scroll-timelines/cancel-animation.html	The cancel event should NOT be fired if the animation is already idle
 PASS	/scroll-animations/scroll-timelines/cancel-animation.html	Canceling an animation should fire cancel event on orphaned element
 PASS	/scroll-animations/scroll-timelines/cancel-animation.html	Canceling an animation with inactive timeline should cause its start time and hold time to be unresolved
-FAIL	/scroll-animations/scroll-timelines/cancel-animation.html	oncancel event is fired when the timeline is inactive.
+TIMEOUT	/scroll-animations/scroll-timelines/cancel-animation.html	oncancel event is fired when the timeline is inactive.
 PASS	/scroll-animations/scroll-timelines/constructor-no-document.html	The source can be null if the document.scrollingElement does not exist
 PASS	/scroll-animations/scroll-timelines/constructor.html	A ScrollTimeline can be created with a source
 PASS	/scroll-animations/scroll-timelines/constructor.html	A ScrollTimeline can be created with a non-scrolling source
@@ -911,12 +911,12 @@ PASS	/scroll-animations/scroll-timelines/scroll-animation-effect-phases.tentativ
 PASS	/scroll-animations/scroll-timelines/scroll-animation-inactive-timeline.html	Play pending task doesn't run when the timeline is inactive.
 PASS	/scroll-animations/scroll-timelines/scroll-animation-inactive-timeline.html	Animation start and current times are correct if scroll timeline is activated after animation.play call.
 PASS	/scroll-animations/scroll-timelines/scroll-animation-inactive-timeline.html	Animation start and current times are correct if scroll timeline is activated after setting start time.
-FAIL	/scroll-animations/scroll-timelines/scroll-animation-inactive-timeline.html	Animation current time is correct when the timeline becomes newly inactive and then active again.
+PASS	/scroll-animations/scroll-timelines/scroll-animation-inactive-timeline.html	Animation current time is correct when the timeline becomes newly inactive and then active again.
 FAIL	/scroll-animations/scroll-timelines/scroll-animation.html	Animation start and current times are correct for each animation state.
 FAIL	/scroll-animations/scroll-timelines/scroll-animation.html	Animation start and current times are correct for each animation state when the animation starts playing with advanced scroller.
 PASS	/scroll-animations/scroll-timelines/scroll-animation.html	Finished animation plays on reverse scrolling.
 FAIL	/scroll-animations/scroll-timelines/scroll-animation.html	Sending animation finished events by finished animation on reverse scrolling.
-FAIL	/scroll-animations/scroll-timelines/scroll-timeline-invalidation.html	Animation current time and effect local time are updated after scroller content size changes.
+PASS	/scroll-animations/scroll-timelines/scroll-timeline-invalidation.html	Animation current time and effect local time are updated after scroller content size changes.
 PASS	/scroll-animations/scroll-timelines/scroll-timeline-invalidation.html	Animation current time and effect local time are updated after scroller size changes.
 FAIL	/scroll-animations/scroll-timelines/scroll-timeline-invalidation.html	If scroll animation resizes its scroll timeline scroller, layout reruns once per frame.
 FAIL	/scroll-animations/scroll-timelines/scroll-timeline-range.html	Scroll timeline with percentage range [JavaScript API]
@@ -1077,5 +1077,5 @@ PASS	/scroll-animations/view-timelines/view-timeline-source.tentative.html	View
 PASS	/scroll-animations/view-timelines/view-timeline-source.tentative.html	View timeline source is null when display:none
 FAIL	/scroll-animations/view-timelines/view-timeline-sticky-block.html	View timeline with sticky target, block axis.
 FAIL	/scroll-animations/view-timelines/view-timeline-sticky-inline.html	View timeline with sticky target, block axis.
-FAIL	/scroll-animations/view-timelines/view-timeline-subject-size-changes.html	View timeline with subject size change after the creation of the animation
+PASS	/scroll-animations/view-timelines/view-timeline-subject-size-changes.html	View timeline with subject size change after the creation of the animation
 FAIL	/scroll-animations/view-timelines/zero-intrinsic-iteration-duration.tentative.html	Intrinsic iteration duration is non-negative