I was running GitLab on a VPS with specs close to the lower end of the recommended requirements and its performance would gradually slow down over the course of the day until pages seemed to never finish loading. Restarting gitlab got it responding properly again, but the whole process would repeat over and over again, so that it had to be restarted every couple of hours just to be able to use it.

I then switched providers, which also came with more system resources, and GitLab was working without any issues right away. It could have been caused by an oversold node at the previous host, or the slightly higher system specs at the new host made the difference, but I've been running GitLab on that new server for a couple of months now without experiencing those slowdowns again.

If you've noticed a gradual slowdown to the point of pages getting stuck on loading indefinitely, then try to up the system specs a bit, as it could make quite the difference.