imported/w3c/web-platform-tests/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-pointer-remove-source.html 

This test is a highly intermittent flake on Mac wk1 
The diff seems to be just a different failure than already expected. 

It looks like this was last updated in https://trac.webkit.org/changeset/242595/webkit

I was able to reproduce this failure using command:
run-webkit-tests --iterations 2000 --exit-after-n-failures 1 --exit-after-n-crashes-or-timeouts 1 --debug-rwt-logging --no-retry --force --no-build -f -1 imported/w3c/web-platform-tests/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-pointer-remove-source.html

history:
https://results.webkit.org/?suite=layout-tests&test=imported%2Fw3c%2Fweb-platform-tests%2Fhtml%2Fsemantics%2Fembedded-content%2Fmedia-elements%2Floading-the-media-resource%2Fresource-selection-pointer-remove-source.html

Diff:
--- /Volumes/Data/slave/catalina-debug-tests-wk1/build/layout-test-results/imported/w3c/web-platform-tests/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-pointer-remove-source-expected.txt
+++ /Volumes/Data/slave/catalina-debug-tests-wk1/build/layout-test-results/imported/w3c/web-platform-tests/html/semantics/embedded-content/media-elements/loading-the-media-resource/resource-selection-pointer-remove-source-actual.txt
@@ -1,3 +1,3 @@
 
-FAIL pointer updates (removing source elements) assert_equals: error events on c expected 1 but got 0
+FAIL pointer updates (removing source elements) assert_equals: error events on b expected 1 but got 0