The notification window at the top of my phone KEEPS coming down on its own and sometimes I can't get it to go back up. This has been the absolute worst phone I have ever owned. Its a galaxy a21 or Samsung a21 one or the other.
Sounds like something is registering a phantom swipe down on your screen -- do you have the phone in a case that might be touching the top edge of the screen? Do you have any sort of screen protector or other material installed that touches the screen?