Coherence has become unusable

Over the past couple of days, Coherence has become virtually unusable (get it?...virtually unusable..ha ha, I kill me!)

Anyway, I'm running a Win 10 VM (Build 14393.321) under Parallels 12 (V 12.0.2) on an early 2016 MPB with an external Dell 4K display and an external Acer UHD display. I've observed the following:
1. Coherence appears to start fine if no windows apps are open (primarily MS Office 2016) but all Win 10 windows are black after opening.
2. If a windows app is open when I start Coherence, I end up with a black display (presumably the window for the open app) that dies not go away as long as I'm in Coherence.
3. Whenever exiting Coherence, I always end up with an oversized window for the VM that exceeds the display dimensions.
4. Operation is generally okay in normal and full screen mode although lately I've been seeing a lot of artifacts in the display in full screen mode that only go away after scrolling the affected area off-screen I'm also seeing seeing shifting artifacts in the upper right corner when in normal mode (I'd attach a video of the condition, but the screen captures created by Parallels Toolbox have extensions that are not allowed for upload...I got nothin'...)

Is there a solution to this problem?

 

Hi @MarkP11
Please try the below steps & let us know how it goes.
1. Uninstall Parallels Desktop 12 for Mac(use PDRemove.zip)
2. Run First Aid on the Mac Hard drive.
3. Reinstall Parallels Desktop 12 for Mac
4. Reinstall Parallels Tools

 

I did that and the fix was short lived. I suspect that it may have been connected with the Windows 10 VM. After deleting the VM and creating a new Windows 8.1 VM, I have not observed the problem again. Sadly, I seem to have no patience for problems like this. It tends to end up all scorched earth and body bags when I run into them. :-(

 

Try these steps

1. Shut down the virtual machine.
2. Open the virtual machine configuration > switch to the Hardware tab > select the Video (Graphics) option in the left pane.
3. In the right pane, increase the video memory to 768 MB then check.