It seems to me that your game is running out of resources/memory. I am always careful to save before going into CAS and try to stay there for the shortest time possible. I have not attempted to stay there for an hour and if I did I would assume a crash would be the only possible outcome.
I've never spent an hour in CAS in one session but I occasionally spend some time when I am creating a new sim. I've not yet crashed while creating a sim but am aware it can happen so I save the sim to the bin when I feel I have made some progress. When I am done I delete the earlier sim files, only keeping the final version.
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Zumi and the Winchester Brothers
The Watcher's Caretaker - A Limited ISBI