If you make it to the Fire Hand unlock without having received the item for it yet, then it is possible to retrigger the unlock cutscene by leaving the temple (so you lose access to the hand) then going back. IF you trigger the cutscene with luigi following you, then Mario gets pushed out of bounds during the cutscene, softlocking the game by preventing the cutscene from continuing.
I did not test with the thunderhand, but i wouldn't be surprised if this can also happen there.
If you make it to the Fire Hand unlock without having received the item for it yet, then it is possible to retrigger the unlock cutscene by leaving the temple (so you lose access to the hand) then going back. IF you trigger the cutscene with luigi following you, then Mario gets pushed out of bounds during the cutscene, softlocking the game by preventing the cutscene from continuing.
I did not test with the thunderhand, but i wouldn't be surprised if this can also happen there.