Some screenshots save while random others don't.

I take a lot of screenshots. Recently, I migrated from an early-2015 MacBook Pro 13" with Retina display to a mid-2019 MacBook Pro 15" with TouchBar. I disabled the ScreenShot application from launching when I perform the ⌘+Shift+4 shortcut to grab a portion of the screen, since I want instant accessibility to the feature without thinking about special details. I also removed it from the TouchBar. I changed its command to ⌘+Shift+5 and it defaults to a window-grab, since I find that feature useful in rare instances.

I still run macOS Mojave 10.14.6. I never experienced this issue on the older device:

Frequently, I will screenshot two visually similar items while shopping so I can compare and contrast them side-by-side later. When 'later' came around, I realized something dreadful was occurring: Several of the screenshots that would have paired with the comparable images were never saved.

Yes, I heard the snapshot sound effect, and the cursor changed accordingly. Yes, I have it set to automatically save screenshots to my desktop. No, I don't use DropBox. I have checked my clipboard whenever I've noticed this happening, in case I had accidentally been using ⌘+Shift+3 which saves to my clipboard, but that was not the case in any instance of this issue.

The only thing I'm doing differently on my desktop is using icon stacks. What could be preventing sporadically taken screenshots from saving?