It is usually their shared runners. I experience outages with them a couple times a month. It isn't a big deal since we maintain our own private pool, so I just move jobs to them. (They make you pay for CI minutes so we use them for certain jobs.)

For me even our private runners stopped worked over the last few weeks

Ouch. We haven't seen that, but we don't run them all the time either.

I use GitLab for my side project (source control only; don't have any kind of CI set up just at the moment) and it's been years since there was any really noticeable slowness for me. I can't say I use it daily, but fairly frequently.

6 months is a pretty low bar for a SCM tool.

Github has had frequent downtime too in the last 6 months too. For a low bar, it seems to be fairly hard to clear.

Same - I've had zero issues.