"This camera has more than autofocus problems. It has ADD."
(Unless you have 20 minutes, skip to 9:49 in the video below.)
The GH5 is a fabulous camera, (this from a Nikon and Sony owner) and the autofocus problem can probably be fixed with a software update. Panasonic is well aware of the problem.
Here's a workaround until Panasonic remedies the situation:
IphoneDo reluctantly sent his GH5 back and bought a Sony a6500, which he even more hilariously reviewed below: