Windows 10 Guest slow down when a screen grabber is active on the host

[Codehunter]

When a screen grabber (like Teamviewer, MS Teams screen sharing, Zoom screen sharing etc.) is active on the host machine (Linux Mint 20), the Guest VM will slowing down more and more and finally freeze.

This is reproduceble in relation with screen grabbing. When a regulary Teamviewer or Teams session is active, the Guest is usable normally. From the moment when I activate any screen sharing, the guest is affected immediately.

At the moment the screen grabbing is ended, the guest is usable normally again.

[Codehunter]

I have accidentally discovered some easy steps to reproduce this issue:

1. You need a two monitor setup at your host machine and a NVidia graphics adapter with Noveau driver.

2. You must configure your VM to a two monitor setup too.

3. Switch your VM to seamless display mode.

4. Open on your host machine an Firefox browser, go to Youtube, play an video, move your browser window to the second screen on your host machine and maximize its window. (Maximize the window is important to reproduce the issue!)

Now your Windows VM will slowing down and shows some silly effects when pasting an text from clipboard. It will pasted multiple times and the text and mouse cursors will toggle between normal and wait style very fast.

When you pause the youtube playback in the browser window, the VM will return to normal work instantly, but only when it is not already freezed.

So i think this issue is related to the Noveau driver and multi-monitor-setups. I guess that Noveau does not have a hardware accelleration for the second screen and will result in a high CPU load when playing a video or grabbing a screen from the second monitor.

I hope this helps to find the problem in VBox. Thanks!

[Codehunter]

PS: I am on VBox 6.1.26 r145957 in the meantime sind I had posted the issue first time but it is still here.