Configuration: Ubuntu 20.04 LTS; Linux kernel 5.4.0-42-lowlatency; GeForce 1060 6GB
Two monitors: LG 27GL850 (144Hz DP connection) and Asus VG248QE (60 Hz single-link DVI connection, despite display could more)
If the second (slow) display is connected then “effective” refresh rate on first (fast) display is limited to 60 Hz. I mean effective, despite xrandr shows 144 because actual window moving traces, effects in 3D games are similar to 60 Hz, and testufo.com also shows 60Hz. If I disable slow display in nvidia-settings, effective refresh rate (window moving stuttering traces, games) are smooth as supposed to be, and ufotest shows 144 Hz and smooth ufo moving.
I remember that there were no such issues with some previous version of Nvidia driver (3xx)
This ticket is similar to Wrong v-sync framerate with multiple monitors having different refresh rates however I don’t use v-sync and xrandr shows 144Hz for the primary monitor