Predator and CL did not provide any possible suspects.
Using Code Search for the file, "SelectionTemplate.cpp" assigning to the concern owner.
Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/ddf851a7d72103c0062bebeb3d3af42b9d5b5c6d

@tkent -- Could you please look into the issue, kindly re-assign if this is not related to your changes.
Thank You.

My CL isn't the culprit.  Route to Editing triage.

Lower to Pri-3, since real world usage of "insertUnorderedList" is very low < 0.003%.

ClusterFuzz has detected this issue as fixed in range 472211:472281.

Detailed report: https://clusterfuzz.com/testcase?key=4650453521661952

Fuzzer: ifratric-browserfuzzer-v3
Job Type: mac_asan_chrome
Platform Id: mac

Crash Type: CHECK failure
Crash Address: 
Crash State:
  position.IsConnected(). UL@beforeChildren in SelectionTemplate.cpp
  blink::SelectionTemplate<blink::EditingAlgorithm<blink::NodeTraversal> >::Builde
  blink::InsertListCommand::DoApplyForSingleParagraph
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=mac_asan_chrome&range=472186:472211
Fixed: https://clusterfuzz.com/revisions?job=mac_asan_chrome&range=472211:472281

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=4650453521661952


See https://dev.chromium.org/Home/chromium-security/bugs/reproducing-clusterfuzz-bugs for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz has detected this issue as fixed in range 472211:472281.

Detailed report: https://clusterfuzz.com/testcase?key=4650453521661952

Fuzzer: ifratric-browserfuzzer-v3
Job Type: mac_asan_chrome
Platform Id: mac

Crash Type: CHECK failure
Crash Address: 
Crash State:
  position.IsConnected(). UL@beforeChildren in SelectionTemplate.cpp
  blink::SelectionTemplate<blink::EditingAlgorithm<blink::NodeTraversal> >::Builde
  blink::InsertListCommand::DoApplyForSingleParagraph
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=mac_asan_chrome&range=472186:472211
Fixed: https://clusterfuzz.com/revisions?job=mac_asan_chrome&range=472211:472281

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=4650453521661952


See https://dev.chromium.org/Home/chromium-security/bugs/reproducing-clusterfuzz-bugs for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 4650453521661952 is verified as fixed, so closing issue.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.