Which version riser are you using? I use strictly 006c ver and oddly have never even gotten a bad one, yet.
I also use the 006c version, everything is stable with them once they are connected properly. I have a bunch of 008s available now so i can test them once i get more GPU.
The issue with those 008s is that the USB connector is pointing in the wrong direction for a B250.
There are 008 risers with straight-out type connectors, but they DO seem to prefer those right-angle things that don't work in most of the slots on this MB.
I've had fewer issues with 008 risers to date than 006c, but my sample size on both sides is pretty small.
Getting the integrated iGPU on an Intel APU to work with anything else under LINUX - forget it, the drivers don't play together.
Under Windows, it's trivial-easy - but I always have a monitor plugged in, or a KVM switch, to that connector.
Perhaps try putting a dummy plug on the connector for remote access use?