Predator and CL did not provide any possible suspects.
Assigning to the concern owner using Code Search for the file, "fx_basic_memmgr.cpp".
Suspecting Commit#
https://pdfium.googlesource.com/pdfium.git/+/2b797295d6851b3189bcb38c5994074f36453865

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

ClusterFuzz testcase 6638919690223616 is flaky and no longer reproduces, so closing issue.

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