Right away, I'd like to lay out my theory regarding my problem: Submitting and closing and reopening a form seems to be a different "thing" than simply submitting.
I have a form that during Form Load sets a filename via the classic userName+now concat. It also grabs and displays a SharePoint ID number on the form via a double submit (Submit, Query, Set ID Field, Submit). Both of these rules run on the condition "is blank", so opening already submitted forms does not change these values. I do this during Form Load rather than the final Submit because this form in addition to being electronically submitted must also be physically printed out; I can't expect users to close-reopen-print-close rather than just print-close.
Now to the issue: Particular users (not everyone) seem to have an odd issue where several submissions are happening in rapid succession. In the attached screenshot we see that we have a 2nd doc created 10 seconds later, a 3rd 7 seconds after that, and a 4th 1(!) second later.
I'm partially able to recreate this problem myself, by starting a new form and then refreshing my browser. Each time I click refresh instead of returning to the same filename and ID it creates a new document again! This seems odd to me because the form has already been submitted to the SharePoint - neither of the rules that create a new filename or fetch an ID number should run, because those values are not blank. And yet, it acts as though nothing is filled in, so it creates a new document.
Curiously, if I add a new document, then close the form and reopen it, I can refresh the browser as many times as I want and it acts as expected - retaining the same filename and ID.
So what's happening here? Why does a document I just created, and has been submitted twice via rules, behave differently than a form I actually close and reopen? My guess is that whatever causes this behavior is what's causing the screenshot issue for my users. Maybe a weak Wi-Fi signal or some browser configuration is causing their browser to "refresh" a few times before settling? Google has finally failed me ;)