hi,
so i went to sanctuary, removed the level 3 general store, created a new general store with a different model, saved and exited.
i then reloaded 4.0.8 simsettlements 3-in-1, so i am now running both simsettlements and conqueror at the same code level.
i started the game, spawned into sanctuary - everything is 100% as it should be.
truly great job zeroing in and finding what i can only assume is an extremely oboscure bug in that model, and that in turn, explains why this is difficult to replicate because it totally depended on the presence of this model being in the settlement.
i continued my verification, and travelled to drumlin diner, then walked back to abernathy, then walked to red rocket - game is 100% stable. i went from red rocket down to the museum and then to the car park at the back of concorde where you can get random encounters, walked to the quarry where you drain it and fight mirelurks - walked up to the robot junk yard and back to sanctuary - no issues at all.
seriously good job to everyone who contributed to tracking down this one.