In the Minecraft Multiplayer Menu, I have found that my servers get randomly deleted from the list, and I have to re-add them manually every time this happens. It's not common, maybe once a week, but it still gets pretty annoying.
How to reproduce:
Although to me it seemed random, I have found that clicking the 'Refresh' button repeatedly does sometimes cause the bug.
It mostly happens when some servers that are online don't appear online on my server list (it says "Can't reach server")
Duplicate of MC-39583 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.