Yes this I encountered as well.
This happens if:
1) your db is corrupted (but this sucks because you can't easily tell since miranda looks like everything is ok
OR
2) you use 32 bit miranda and your DB is large (200-300+ MB). The compaction loads the whole profile and spits it out into a clean profile and I think the 32bit mdbx cannot map so much. The max is around 430something megabytes (not sure what the exact number is).
So unfortunately known but hard to predict when it'll happen. I've simply stopped running compaction altogether for now.
Moreover if your db is corrupted and you compact, even 64bit miranda will make it into a 1MB and bye bye data.
