Only two things:
I haven't experienced that so far. Using my GFX for nearly a month every day now. So I wouldn't consider this a "normal" error.
I had the same experience, though, with my then brand new X-Pro2. I heard different stories about the reason: broken/weak battery, hardware failure, firmware. Some people reported, the this never happened to them, some, that they have it all the time. Since one of the first firmware updates, it never happened again.
My theory is, that Fujifilm programmed the firmware very near the limits of the hardware. More efficient programming, bugfixing and so on in later firmware updates may avoid these pitfalls and everything goes away. Also the firmware programmers have to learn how to handle the hardware.
Anyway, if this is a reproducible problem, contact either Fujifilm or your dealer. They should handle it...