Ok, for now the game crashes for me with one specific ship ONLY when I attach a rover subassembly inside a Service Bay (2.5m), as Scott Manley does in his career mode video :
BUT, rather than attaching it with a decoupler as he does (works for me too, without a crash ; EDIT: Crashed today), I'd attach it with two Jr. docking ports. Then my game crashes as I revert. If I place the rover anywhere else on the ship, it doesn't seem to be a problem. Collision/physics problem then? The plot thickens.