@jonne@infosec.pub is right about the .ml part, as for vlemmy, one day it just stopped existing. nobody knows why. some people are theorising that the admin did not want to moderate and shut the instance down.
The rules set by the registrar are that any ml domain needs to be used for something relating to Mali. Presumably you could run a Lemmy instance that has a focus on Malian content and keep using the domain within the rules, but the way Lemmy.ml was using it was obviously not.
.ml top-level domain got taken back by the Mali Government ".ml" stands for Mali
Edit: lemmy.ml is still up either because the Mali Government haven't gotten to them yet (lemmy.ml is after fmhy.ml in alphabetical order) or maybe they paid for the domain instead of getting a free domain like lemmy.fmhy.ml did.