Stutter scrolling Sapphire Radeon Vega 64 Nitro+ Mojave

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I have very good results on highSierra with my Sapphire Radeon Vega 64 Nitro+.
Scrolling in Safari is very smooth, Cinebench is good.
And this on both my monitors, ASUS MX27UC and Dell U2713MH.

However when I update to Mojave scrolling on my 4k monitor in Safari (or Chrome) isn't smooth anymore, every 3 seconds the 'page' stops and then it jumps up a bit.
It feels like scrolling is continuing in video memory but isn't flushed to the screen for a very short moment.
Cinebench does the same, every few seconds the screen isn't updated and then the same 'jump'.
The same page on my Dell monitor is not affected, stutter only occurs on my 4k monitor, both monitors are connected with DP.

Same EFI folder, just updated to Mojave.

Any ideas?

 

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This stutter is not always there, and when it happens putting the computer to sleep and wake up again makes it go away.
Then scrolling is smooth.
Very strange, the recent updates didn't fix it.
I tried to narrow it down to an app I use but no success.

Am i the only one with this problem?