Wow I wish I knew!  It looks like you tried everything.  ???

I have a troubleshooting strategy I call "start with something that works" - the 507 in the logs makes it look like the device mount check is failing for some reason - but you can disable that:

Does it "work" if we turn off the mount check entirely?  Have you been able to configure swift successfully in the past on *different* hardware or software configuration(s)?