Battery pack losing contact because of the rumble motors is the most likely reason. You should notice a small piece of plastic protruding out of the controller into the battery case. This closes a contact on the normal battery packs and it's that contact
point that might need mild cleaning, or a small piece of paper to put even more pressure on that contact. On the rechargeable packs the contacts might need some simple cleaning and a rubber eraser works well enough for cleaning copper contacts.