Sleep mode stopped occurring automatically

You're welcome.
Glad to hear it's working :)

If I may, I have one more question: if it ever turns out that there's some reason to re-allow the request, is there some way to do that?

Yes, but that's not documented in the powercfg help ...
I'll find the instructions and post back.

Here is the command to remove that override
powercfg -requestsoverride DRIVER \FileSystem\srvnet

The last parameter (system) in the command to set the override is removed from the command to remove the override

Here are the 2 commands - 1st one to set the override, 2nd one to remove the override

powercfg -requestsoverride DRIVER \FileSystem\srvnet system
powercfg -requestsoverride DRIVER \FileSystem\srvnet

Thanks again!

I have something interesting to report. Just to test, I removed the request override and tested to make sure it was removed. Then I thought I would see what happens if I just left my computer to go to sleep on its own, and to my surprise, the problem seems to have resolved. I haven't yet tried it in every possible situation, but it seems good.