I am not sure whether this is the same issue, but I get freezes within ~1 hour
uptime with the latest firmware (18.40) on a Ryzen 2500U (Lenovo E485) with
4.20 rc3. I will attach a dmesg log of such a freeze.

I did not see freezes since weeks, but they reappeared after upgrading the
firmware from 18.30 to 18.40. Moving between different kernel/mesa/xorg driver
versions did not help. I am now back to the 18.30 firmware and did not see a
freeze within a full work day.