Just wanted to give you an update on my situation. The USB disconnects in my machine had meanwhile come back and became even more critical. Also compared to how strong they were in the beginning. And in addition after a while also my graphics adapter created black and blue-screens regularly and always directly after I heard that typical Windows sound when a USB device disconnected.
Sometimes I had to restart my PC ten times before it ran stable at least for some hours (and only by hard resetting it). Benchmarks were all fine. I stress-tested the CPU and the RAM. Ran PC-Mark, 3D-Mark, Furmark and all of that w/o problems (but of course each time only after I got the machine running properly).
I updated all drivers, the boards firmware, etc., even the firmware of my monitor. Nothing helped. In the end I decided to replace the board and ordered an EVGA X570 FTW which arrived last week. Over the weekend I did an "open heart" surgery on my PC, replacing the motherboard. And voilÃƒÆ’*, now it runs as smoothly as you'd expect it to be. Will now get in contact with the retailer in order to find out what to do with the Dark Hero board. It should still be in the warranty period.
I always trusted Asus as a premium brand. I don't know what they were thinking releasing such a crappy product. I have many other hardware components from Asus that all work fine. But this was a great disappointment.