Precision 5520 (with TB16), U3417W and AutoCAD

I have Dell Precision 5520 with NVIDIA M1200 (and TB16) connected to U3417W through dock's miniDP to display's DP. When I start using AutoCAD 2019, fans go on full speed, even though GPU temperature is normal and mouse is moving like in slow motion (not sure how exactly to describe it). I have not yet installed Win10 May Update, but all latest drivers should be installed.

Problems started as soon as I got U3417W, which I have had over a year.

I tried to use display without dock, using HDMI cable, still the same problem. I also have 24" Dell display, with this, there are no problems using AutoCAD.

At first I thought dock (TB16) could be faulty, but if the problem is still present without it, then it's either GPU or U3417W. I have yet to try it with another ultrawide, because I don't have any other close by.