The AXTextMarker*Refs can be released on the AX thread and hence be invalid on the main thread.
<rdar://problem/104881175>
Created attachment 464783 [details] Patch
Committed 259918@main (e0e146fe111c): <https://commits.webkit.org/259918@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 464783 [details].