According to mpv manual
--save-position-on-quit
Always save the current playback position on quit. When this file is played again later, the player will seek to the old playback position on start. This does not happen if playback of a file is stopped in any other way than quitting. For example, going to the next file in the playlist will not save the position, and start playback at beginning the next time the file is played.
This behavior is disabled by default, but is always available when quitting the player with Shift+Q.
mpv behaves according to documentation and resumes playback as intended.
Gnome-mpv stubbornly refuses to resume from the last position: configuration files, the option check from preferences, the extra options from the miscellanous tab all get ignored.
If launched from the command line I get the message "Option --save-position-on-quit unknown".
Am I doing something wrong or it's a bug ?