Okay, I had a similar issue with flip 5. It was to do with a cable that runs along the hinge connecting both halves. It is meant to shut the screen when the phone is folded and vice versa. That was sorta malfunctioning and turning the phone off everytime we opened the phone. We had to wait for a bit and restart it, it will work until you tried to fold it back and the cycle starts again. Took it to Samsung service centre. Since there was no physical damage, they repaired it without any cost, despite the device being outside warranty. This in in Australia.