I am not sure where to start to find information on this but I am going to post a video, and some code for help asap please.
I have a tank I made. The top needs to swivel, which I can do that. I have the top in its own spatial scene. Here is the heirarchy of it:

So, I have a main script for tank control, etc. I also have a script inside the top, that makes it shoot. Here is the info on that:
pic of the main script[part of it] above The tank DOES USE INTEGRATED FORCES and is made to move only for such.
The other part, the top (WHICH IS PART OF THE CAMERA btw) [the camera has no problem staying attached) is here:

So, here is the TOP scene attached to the tank main camera(because the camera swivels with it):

And Ill show a video link :
VIDEO OF IT HAPPENING AND ALSO WORKING
Now here is the issue---The top does not always stay connected to the tank! I can make this happen when I enter the tank and try to move the tank. I am not sure if it is random yet, or based on some action I do that causes it to not move, versus when it actually does work.
IN THE VIDEO: notice also that the top is not collidable like the tank? I made a heli with the exact same setup to test what is wrong but the heli gun works, as in STAYS ATTACHED, even with the same types and heirarchies. So that is why I am baffled.
Ill post more answers upon questions if needed :) Thank you very much if you can help and it, as usual for most of the time, may be something simple! Heli is in air, and tank is not so idk if that makes a diff. But my only thought left is physics control.
Let me know what you think please and ty