Patch Tool Issue -- Parts of image disappear when using Photoshop 21.1.2 macOS 10.13.6

Hi everyone --

I have been stumped at how to solve this strange occurence the past few weeks. I use the patch tool a lot for retouching and only recently had this reoccuring issue with parts of the screen going black when I am dragging the patch tool, which is super frustrating since often times I need to see the rest of the image to edit. I attached a video to show the issue because I haven't found any luck in the forums. Please help 😞 

Please Note-- In the video I am just dragging to show the parts that disappear (I circle these areas at a few points in the video with the cursor)-- the sampled areas are not indicative of an actual edit / the issue at hand; screenshot attached also

Not sure if this is necessary but just in case, I am using

Mac Book Pro / macOS High Sierra (ver.  10.13.6) / Photoshop CC 21.1.2

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