HP Prime does a soft reboot whenever I set it down

[Tim Wessman]

Your battery is losing connection. A very simple fix is to open the battery door (two small screws on the back, will in no way void warranty) and check if there is a strip of foam on the inside to "press" the battery down. It might have been missed. If it was not, put a few pieces of tape on the inside of the door to press it down/in more and I bet the issue goes away. Battery sizes are never 100% identical and yours might be slightly thinner in a dimension.

A tiny bit of padding to push the connections more firmly to the pins (or a tiny roll of paper at the bottom to push it upwards) to the top to ensure it does not wiggle in there and you can close it up and never worry about it again.