On Tuesday March 30, 2021 around noon, I applied some new "fixes" to the website in an attempt to stop the logout problem. Please let me know if you experience problems after this date.
Here's the problem: You are logged in and chugging along doing stuff when the system tells you to log in again. And again. And again... Very frustrating!
Previous fixes haven't worked. I've done a "workaround", by clearing a couple of system cache items - this works for a couple of weeks, and then the problem appears again. So I have to do the workaround again.
The support site for phpBB, the underlying forum software, did not have any answers, except for some dumb system admins who badly mis-configured their forums.
A month or so ago, I built a test forum, with a much newer version of phpBB. This would eliminate any problems associated with the ancient version of phpBB we use - because of the "send email to everyone" feature which is important for a small audience like ours, but not wanted on a large busy site, and therefore dropped from future phpBB versions. The newer version also eliminated a couple of other possible problems that might be related to our specific web hosting environment.
This "upgrade" looked like it had solved the problem, but after a few weeks of testing, the test forum also exhibited the logout problem. Dang!
FINALLY, I found a couple people who were having similar problems, and are using Cloudflare - an anti-hacker tool which we use on the recommendation of our web host. They changed a certain system setting, and it looks like that fixed their problems.
Will it fix ours? Keep your fingers crossed!