Phantom Breakpoints Driving me insane!

This makes no sense to me:
I am running a vba-based program to update a number of files.
The code seems pretty simple, if not done with best practices .. as I got code suggestions from a number of places.

Anyway, it was all working fine!!!!!
So, I assume that the code was pretty much OK, eh?
Then it would stop working.
So then I would make changes to try to fix it.
So, I can't say that I've made NO changes but no changes that I'd expect to have such drastic outcomes.
And then only to fix the disruptions.

As an outline:
There is a summary file that has a list of all the data files.
The objective is for the summary file to call the data files in sequence, have them get their respective updates and close, returning to the control of the summary file vba.

Right now the outcome is that the summary file stops (with "Code execution has been interruped: Continue/End/Debug/Help")
at an End If statement but will continue with either F8 or Continue.

Then it stops with the same interruption again at the beginning of the next called workbook Private Sub Workbook_Open() statement.

Selecting continue bounces between these two interrupts.
Using CTRL-SHIFT-F9 seems to do nothing.

This is very bad because I can't get code to just execute normally - except perhaps by accident. Then, again by apparent accident it stops working again with non-predicatble results.

I have no idea how to proceed at this point.