I've identified where the error is occuring but I still don't understand why.
Also, I mispoke in my second post the running sum is in the grouping footer
next to the subreport (also in the grouping footer). So for one of my
records it is picking up half the amount. It shows the total for the record
to be $1000 but only adds $500 to the running sum. The record is the sum of
two $500 amounts. It is not the only record with two amounts so it's not
happening every time. This is baffling.
I'm using a subreport that also has a subreport. Everything works correctly
when visible just not when invisible. Just so weird.