Jenkins cli hangs sporadically

Jenkins setup: 2.440.2 on Win 2019, JDK 17.0.9
Pipelines and non-pipelines (running python, ansible, etc)
We have another app that submits builds using the CLI jar over websockets. Out of several hundred jobs in a day, we get a handful (say 10) that seem to “hang.” The calling app just sits there (never returns) but there is no job running. If we kill the job from the app and rerun, it works OK.

Additional info: we recently upgraded from a very old version of Jenkins - copying the folders from the old server to the new. I originally thought it was quiet period related (due to some error messages in the logs), but I tried setting the quiet period to zero and we still see the behavior.

Anyone have any ideas?