My game crashes periodically when building a 3rd room that would merge with a double room. My vault is large, 170+ dwellers with nearly all levels filled with rooms built and rarely crashes, but when it does it typically is triggered by building a 3rd room that appears momentarily as a single room beside the double room before the crash. On reopening fallout shelter it has loaded to before i built the 3rd room and also after with the rooms not merged appearing as a single beside a double.
I consistently had issues with living quarters repeatedly crashing and managed to succeed in building the rooms i wanted after successive crashes by upgrading the double room, building a single room beside it and then upgrading the single room to merge. This also crashes, but it seemed less often.
Other than consistent issues with building living quarters, i have crashed while building a 3rd of other types of rooms, but not as often.