gThumb hangs when some mount point is unavailable
This bug seemingly exists since 2015: https://askubuntu.com/questions/609698/gthumb-freezes-on-start
When there is a mount point which gets unavailable for some reason, gThumb hangs at start. Other people had this problem with mounted webdav and/or iphone. Personally i had this issue with samba shares. i have mounted a Kodi share and after reboot of the Kodi box i could not view any local pictures until i unmounted the (offline) share.