It doesn't seem to be related to a certain GCN generation, as there are exactly
matching reports of at least Hawaii, Polaris 10/11 and Vega 10 (probably also
Fiji).

It probably neither is related to the type of display output, as I am using
DL-DVI and grmat afaik uses Display Port.
And I suppose we all tried standard refreshrate of 60Hz without success.

So, unfortunately, I am rather clueless.

But I just noticed we haven't yet followed David's idea of setting a low
"standard" mouse polling rate of 125Hz.
I currently don't have my Radeon installed, so I can't give this a quick try
(but can do so in the future).

Does anybody have this issue with a native resolution of 1920x1080 60Hz? I
haven't tested such a display yet.