I have had the same issue since I first started using MineOS (years ago, at this point).
For me, I found that if the worlds had lots of restore points, or archives, they would take far longer to appear in the server list.
Unfortunately, I haven’t found a solution to this, other than manually deleting a bunch of the archives and restore points, which kind of defeats their purpose, I know. I had asked previously about enabling an auto-pruning feature for them. Something like:
For the first day, keep snapshots every hour.
For the first week, keep snapshots every day.
For the first month, keep snapshots every week.
And so on, so that there isn’t as many of them.
I’ve recently upgraded my server quite substantially performance-wise, and the issue has been lessened quite a bit. The UI still takes about 5-10 seconds or so, but it’s down from the 30-90 it could take previously.
For reference, I currently have nine servers, seven of which are online, with maybe 20-30 restore points and a couple of archives each. This is running on an unRAID Docker instance, with 2C/4T of CPU allocated, and however much RAM it wants. I think it’s using about 6GB currently.