Mojave graphics problem when PCIe RAID card is plugged

[benjiolino]

Hello everyone,
yesterday I installed Mojave and a Saphire Pulse Vega 56 in my setup. Everything went smooth until I replugged my Highpoint RocketRaid 2720 card into the second or third PCIe slot. When I do this the machine boots up to a black screen with cursor and some strange red dots. Sometimes it showing the desktop partly in the middle of the monitor. Please check attached image. When I unplug the card again it boots up normally.
My setup in the moment is:
Mainboard: Gigabyte Z170xp SLI
Graphics: Saphire Pulse Vega 56
CPU: 7700k
I use the Highpoint already since years with macOS 10.11, 10.12 and 10.13 and it always worked fine. Its normally recognized as a hard drive not influencing the booting up.
If anybody has an idea how to fix this I would be very happy. I want to upgrade to a 9900k that's why I want to run Mojave.
Best