I'm very curious to hear what they have to say.
So they helped fix it but it had nothing to do with them or their plug in.
Gregor,
Our plugins don't even exist in memory while Photoshop is in an active state.
Our plugins have to be called by Photoshop and we don't generate any type of floating menus or toolbars as our plugins are windowed apps.
I'd suggest you delete your Photoshop preferences on your next Photoshop load and/or update your video drivers.
Also, if your mac has a discrete/integrated video card combo this has been known to cause graphics issues like yours.
This Apple KB goes into how it works:
https://support.apple.com/en-us/HT202053
I use this small app on my MBP's from time to time to manually switch from integrated to discrete:
https://gfx.io/
Regards,
George
It was the deleting photoshop's preferences that seems to have done the trick. It had the fringe benefit of resetting the palettes to a nice dark gray which I must have forgotten was possible.
So there you go - a mystery for the ages solved.
Gregor
PS: In case this ever comes up again...
Resetting Photoshop's Preferences (All Versions)
To reset Photoshop's preferences using the first method (which works with all versions of Photoshop), the first thing we need to do is quit Photoshop. To do that, on a Windows PC, go up to the File menu in the Menu Bar along the top of the screen and choose Exit. On a Mac, go up to the Photoshop menu in the Menu Bar and choose Quit Photoshop:

Go to File > Exit (Win) / Photoshop > Quit Photoshop (Mac).
Then, with Photoshop closed, press and hold Shift+Ctrl+Alt (Win) / Shift+Command+Option (Mac) on your keyboard and relaunch Photoshop the way you normally would. Just before Photoshop opens, a message will pop up asking if you want to delete the Adobe Photoshop Settings file (which is your Preferences file). Choose Yes. Photoshop will then open with all of your preferences restored to their default settings:

Choose Yes when asked if you want to delete the Settings file.