Ah, a change in GPU would definitely explain why you didn't have any issue before (there was no change at all to the display code between Dear Clockmaker and Zendo).
Are your drivers up to date? Because that really looks like a driver bug...
I've tried a small change to the display code that you could download independently from the game (can't update during the voting period), to see if perchance it fixes the issue: https://drive.google.com/file/d/1JDK0C7XWdVYmRBNPWErXcoVtMRglyu17/view?usp=drive... (download that file and drop it in the same folder as Zendo.exe, overwriting the existing version). Though I'm not very confident it will fix anything, because the code looks correct and does work on every other GPU I've encountered so far :/
If you try it, please tell me if it changes anything. Thanks!