This started happening around the time I started using GOG galaxy.
When I use the website, it remembers my account credentials, but wants me to enter my password and log in manually. Every time. It's not a cookies/browser issue because I have it across multiple systems/browsers.

This is very inconvenient, am I the only one experiencing this issue?

It actually happened to me just recently. I know you don't think it's the cookies, but try purging the GOG cookies, close your browser and log back in. This fixed it for me.

It is the cookies. GOG made a change a while back (right around the release of Galaxy) that seemed to cause a problem with legacy cookies from before the change. If you delete the cookies and clear your browser cache, the issue should go away.

I thought it was logging me out on my cell phone, but it only kinda half-way logs me out. Along the top, it says "login or sign up" where my Account tab would be....but if I link directly to "My Recent Posts," it shows the topics I've participated in.

Really weird.

I fixed this problem by logging out for real and logging back in. Problem never occured again after that.

Resurrecting this because it keeps happening to me whenever I try to like a review.

I'm using latest FF, with all addons disabled on GOG. I don't use Galaxy, only the browser. I can login to my account normally for any action except liking reviews on any game.

I've tried removing all cookies and clearing the cache, and I allow all GOG cookies, but still no luck.
Any advice?