Answering my own question, I did an experiment and tried adding a new user
(while working) and upgrading and could still log in. Based on that, I
updated my user password while working and upgraded, and it worked. So
maybe something about how the old passwords were stored/encrypted.
Anyways,
I asked about this a couple months ago but did not have time to really dig
into it then.
I am currently on Jenkins version 2.265 with the latest version of all
plugins (that I can update). When I upgrade to 2.266+ (have tried with
latest), the server restarts but my user login no longer works
