periodic backups of the session file
Maybe I've missed something when set preferences in 5.6, or perhaps "Make periodic backups of the session file" is not the same than before?
Anyway, have choose it (guess it's default), and launched the actual session in progress. Edit it around one hour, and then Ardour crashes.
When re-launch, all changes are lost. No .history or .bak file at different timestamp than the .ardour one, no "recover data" stuff at launch, nothing but a solitude moment!
Maybe a bug on this particular machine?