Another possible python3.9 regression, mercurial spins but never wins?

[Henry S. Thompson]

TL;DR:
After recent update to 3.9.18-2 I couldn't pull, running on Windows
10, latest cygwin1.dll.  Reverting to 3.9.16-1 the problem goes away.

  >: hg --debug pull
pulling from https://markup.co.uk/hg/xemacs
using https://markup.co.uk/hg/xemacs
sending capabilities command
markup.co.uk certificate matched fingerprint [redacted]
query 1; heads
sending batch command
searching for changes
all local changesets known remotely
sending getbundle command
bundle2-input-bundle: with-transaction
bundle2-input-part: "changegroup" (params: 1 mandatory 1 advisory) supported
adding changesets
add changeset f3ab63e5c39f
[stuck, hard to kill, manager shows 10--20% CPU]

Server python/mercurial installation hasn't changed.

Server logs show no errors, finishing with a getbundle request that
has completed successfully.

Is this related to other already-signalled problems?

ht
-- 
       Henry S. Thompson, School of Informatics, University of Edinburgh
                10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND
                           e-mail: ht@inf.ed.ac.uk
                      URL: https://www.ltg.ed.ac.uk/~ht/
 [mail from me _always_ has a .sig like this -- mail without it is forged spam]