Is this issue still unresolved or can it be closed meanwhile?
I just tried the packaged pure-maps in v22.06 SP2 which pulled in osm scout server as dependency. After downloading the maps via OSM scout server Pure Maps seems to work offline quite well for me so far (did not try navigating with GPS yet, just calculating routes between two points).
This is a pretty old one.
If I remember correctly we never found out what triggered the "Server stopped" issue.
However, as far as I remember it was consistent. So if it doesn't happen to you pretty much immediately after restarting your phone at least once, it is most likely fixed.
I would just close the issue. It can always be reopened.