They're probably leaving due to all the problems this instance has been having. I've only just recently been able to log back in after several days of it just refusing to let me in. Although I'm not sure if it's an instance issue or a Lemmy issue since mastodon.world has been working just fine with no issues.
delete the cache/cookie data for lemmy.world in your browser settings. Directly after the hack everything was working mostly fine for me but if I would open comments in a new tab instead of the one I was already in it would log me out and I was unable to log in. cleared my cache/cookies and logged in again and I'm back to being able to open comments in a new tab without issue.