Did you get LMMS from an (L)ubuntu repository ?
If so, first thing to try is this LMMS version:
https://lmms.io/download#linux
1.2.2
Make this file executable then double click the file to start LMMS.
If so, first thing to try is this LMMS version:
https://lmms.io/download#linux
1.2.2
Make this file executable then double click the file to start LMMS.