""Failed to load mods: Error in assignID: space-location with name 'none-factory-floor' does not exist.
Source: factory-architecture-t1 (technology).""

If I load Factorissimo 3 with APS, this error prevents the game from loading. If I disable APS, Factorissimo 3 works fine.
I was using both mods successfully for at least a week, so I assume something with the newest update(s) did this, but I'm not pointing fingers. I'm no coder.
For now I'm just removing APS to fix this since I ended up starting on Nauvis anyway with my current save, but I figured I'd mention it in case it affects others. Both mods are popular enough that I imagine it could happen to other players. (Unless this error is somehow my fault, I won't discredit the possibility lol)

Can confirm, needs to be fixed. APS broke something. Version 1.1.11 is the culprit

I have discovered that when an alternate starting planet is chosen, the game loads.
But when the starting planet "None" has been chosen, which to me would mean starting on Nauvis, the game crashes on startup with Factorissimo 3 enabled.
Allowing to chose Nauvis instead of "None" would likely clear the bug.

If you wish to start on Nauvis, I suppose a workaround would be to remove Factorissimo 3, start the game on "None", change the starting planet to i.e. Gleba, then add factorissimo3 and load the game which has already been started on Nauvis, but this should be fixed, though.

This is an error with Factorissimo 3, not this mod. I've already been in contact with the mod author about it, it should be a simple fix.
That being said, why would you install this mod and want to start on Nauvis? Just disable this mod, starting on Nauvis is already what happens when you play the game normally. Also, "None" is synonymous with Nauvis, The only reason it exists is so I don't show bias towards any of the planets. I could just remove None and any edge cases caused by having None/Nauvis would go away completely, but I don't really want to do that for a couple other reasons I won't get into here.

I've just received word from notnotmelon that it's fixed on Factorissimo's side now.

"why would you install this mod and want to start on Nauvis?"

Because there are other mods which depend on this mod. Mods which add planets, and then require this mod to choose starting planet. I would like to add planets, but still start on Nauvis. I would suggest replacing the word "None" with "Nauvis". "None" causing the crash made it seem like whatever variable it adjusts is set to nothing instead of a value.
But please do not remove Nauvis as an option, because other mods include this in their list of dependencies, and in order to use those mods, one has to have this one, but may not wish to alter start planet.

"I've just received word from notnotmelon that it's fixed on Factorissimo's side now."
Wonderful! I'll check it out :)