It does sound like something mechanical is loose inside your gimbal. Replacing the ribbon cable might help, but since it was rock solid for the first 5 minutes, Im thinking it's a loose ribbon cable power connection to your gimbal PCB from the gimbal. You can check if the gimbal flat ribbon is all the way clicked in the the gimbal PCB. It might just be a little bit loose and causing a disconnect.
You can use this flexible, vibration proof and water proof sealant It works well because if you end up putting too much on, it peels away just like the OEM silicone.
Most Walmarts sell it in the tool departmetn:
https://www.walmart.com/ip/Loctite-...35&wl11=local&wl12=21674360&wl13=2154&veh=sem