It is a very weird Joplin behavior: after some random time after start, it stops saving changes. If I try to switch the note it just shows blank edit and preview screens. After the restart, it's ok for some time again.
Joplin for Desktop
Joplin 1.2.6 (prod, Linux Mint 20)
Changes: f5f117c (master)
JS console messages. No errors/warnings in log.txt.