J1900 freezes - not on older versions

I had good experiences on installing leap 15 on a celeron j1900 based router, it ran stable also under KDE. Based on that experience I got a supermicro x10sba motherboard, also based on a j1900. However, that motherboard freezes after a couple of hours. I tried with the current Ubuntu version and Tumbleweed 2019 01 15 because they have newer kernels, but same problem. However, the board runs fine on opensuse 13.1 or windows 10. It also works under leap 15 if I run it as multi-user such that kde never starts. The logs never show a trace of the freeze. I read on several fora that j1900 has problems with the power management of the built-in graphics processor but I never had problems with leap 15 on another j1900 based system. Anyone has an idea why it works on 13.1 and not in leap 15 and later?
Many thanks