Performance issues with Qt 5.12.1 and dual monitor setup

[spectralcode]

Describe the bug
When compiled with Qt 5.12.1 processing performance drops significantly on a system with a dual monitor setup, but just if OCTproZ is displayed on the monitor with DisplayPort connection. If displayed on the monitor with HDMI connection there is no drop in performance.

With exactly the same settings as described in performance.md perfromance drops from about 2.4 MHz A-scan rate to 1.4 MHz A-scan rate with the gaming computer setup.

When compiled with Qt 5.10.1 there are no performance issues at all.

To Reproduce
I don't know what the crucial point is for this bug to occur, but on this specific system the bug can be reproduced as follows:

1. Have a dual monitor setup. One screen with HDMI connection and one with DisplayPort connection.
2. Compile OCTproZ with Qt 5.12.1
3. Run OCTproZ and move it to the screen with DisplayPort connection

Used hardware

• OS: Win 10 64bit
• GPU: NVIDIA GeForce GTX 1080 (CUDA 9.1)
• Screens: Samsung T24C350 (HDMI), ASUS VG275Q (DisplayPort)

Additional context
I really don't know what causes this bug and would be grateful if someone with a similar software or hardware setup could share their observations.

Followup March 22th 2022:
There is a performance drop with Qt 5.12.12 and displayport monitors as well. This is particularly noticeable when rotating the volume in the 3D view, as it does not react as smoothly as it should and a lag is noticeable.
There are no issues with Qt 5.11.1