Sounds kinda plausible but as my working drive is internal, it kept working all throughout. I also searched for the project name, just in case - no hits.
Besides, why would Logic go back to the first saved version created straight after booting? I must've saved around 100 times or so (pressing CMD-S is second nature to me since decades). It could as well have returned to any other version but it was just the one I had opened when I was shutting off Logic and the computer the day before.
Anyhow, from now on I will always manually save a new version after each relevant round of edits - I'm sure that even if the autosave function would be on (which is another gripe - I mean, an update usually should keep your preferences), there'd be no "revert to" options, simply because the only existant project file was way old.
Fwiw, Mojave in general seems to be quite a bit less stable than High Sierra. For instance, it sometimes "forgets" to activate USB ports/devices and one of my interfaces doesn't always properly wake up from hibernation - none of these has ever been an issue with HS. I've also had a Logic crash or two when using Battery 3 - which is a pity because NI completely messed up version 4 IMO, but it seems I need to get along with it now.