I installed the latest version of GMB on LinuxMate 20.2 MATE.
GMB is automatically started on system boot.
When I right click on a song and do "Open folder", GMB quit.
But if I restart GMB, then the problem does not happens again.
I notice that this only happen if GMB start on system boo. If I start GMB manually after, the problem does not appear.

This is quite strange.
How can I know what is the source of this bug ?

Thank you for your help.

It's weird. One possible difference when started on system boot is that some environment variables might be different, but I don't know why it would cause a crash.
If it still happens (sorry for answering so rarely and so late) maybe try to find the error, it may be logged in ~/.xsession-errors or maybe look for an error in /var/log/syslog.
Alternatively, if it is a problem with environment variables, you can look at them in /proc/PID/environ where PID is the pid of the process, add some line breaks and compare when started from boot and when not.