On another thread I posted confirmation that this problem can definitely be caused (on my PC, at least) by the Google Chrome Elevation Service. See https://answers.microsoft.com/en-us/windows/forum/all/signed-out-of-everything-on-reboot/4abe91e9-d351-4b45-b79d-bd9a1dc85f45?page=9
The downside is that this Elevation service is part of Google's mechanism for updating its software. It would need to be periodically re-enabled to update Chrome (and possibly other Google software).
While I am 99.9999% sure from my testing that this does cause the problem, there could be other causes.
Many software providers are going to automatic updates these days. It is part of the SaaS model. It may be that deleting login cookies is thought to be a necessary part of the process in some instances for technical or security reasons.
Thanks to Iootin for alerting me to this thread.
As you suggested in the thread you linked, I installed firefox and am using that instead of edge/chrome/opera, and that seems to have completely solved the problem! Thanks so much!