If you want to you can try and copy file by file and folder by folder from _ardour7 to ardour7 and see which is causing the crash, and then see if you can spot any difference between the working file and the crash inducing one.
And then report that in the bug report.
My immediate suspect would be some file in the plugin_metadata folder, but that’s just a guess.
So after a few try, it’s not the config files it’s more of a Ardour-Jack issue it seems.
When the session crashes, I can launch it with my internal soundcard (wich is what was happenninig when I clean the config files). Then I will restart with my regular soundcard the session will work fine.
I also replace file by file and folder by folder my old config files into the new one with no issues.