Scrubby Zoom Randomly Turns Off, Interrupts Workflow

I've been having this problem for months, but I'm getting pretty fed up with it. As a digital painter, the scrubby Zoom is essential to my workflow. Only, it seems that randomly it will be disabled for certain files, or with certain new canvases, and it will suddenly revert to the default zoom, so when I go to Zoom, it will suddenly enlarge by 1000% and I will have to hold ALT and back out 10-15 levels before trying again. I can go back and forth between two different files, and the scrubby zoom will work with one, and not the other. In the latter, the option box is greyed out. 

I have seen other forums with solutions relating to the OpenGL, video card settings, etc. I've reset my preferences, at the expense of hours customizing preferences to optimize my workflow, still nothing. 

I'm using Photoshop version 21.1.3., on Windows 10, 64-bit. I tried updating a couple of months ago but the new version introduced so many new issues that I had to revert, losing all my settings, which took weeks to restore manually. I'm done with Photoshop updates, as they always seem to mess with my settings and create more problems for me. 

It seems like a small issue, but considering that the success of my work depends on an uninterrupted flow state, having to constantly adjust to this apparently random setting change presets a bit issue for me. I would greatly appreciate any assistance on a finding a permanent solution to this issue. 

Thank you,
Eben