I part change all the time… I’m the opposite OT user that does everything backwards from the other users, I use my 4 parts per bank then move to the next leaving a bunch of empty patterns behind…
Part changes need trigs to kick them in. If you do them when stopped you need to double stop to kick em in… For good measure, whenever you stop, double stop, if the sequencer is running, triple stop. The first one stops the sequencer, then the double stop fully sets in the part.