Ok this is somewhat a weird one.
Column filter behavior when using flow variables is a bit awkward.
I did some tests and managed to get it work for the first iteration when I passed the exclusion columns (manually generated them for first iteration) as flow variables in addition to the inclusion columns - this worked!
I then copied the workflow and removed the inclusion columns keeping exclusion columns and this also worked!
I then took a closer look at your configuration of column filter BEFORE passing in the flow variable and noticed that the option “any unknown column” was in the “INCLUSION” box.
I removed the flow variable for inclusion in your initial workflow, moved “any unknown column” to EXCLUSION box, added back in the flow variable only with inclusion columns and voila - the workflow runs through.
tl:dr:
If you pass columns to include via flow variable, “any unknown column” must be in exclusion box
If you pass columns to exclude via flow variable, “any unknown column” must be in inclusion box.
So in your case it needed to look like this before configuring flow variable with inclusion columns:
Workflow: Green box on the right works - the other one’s are experiments for reference…
compareMD.knwf (198.5 KB)
I have to admit as awkward as this is I think it is an improvement from sometime in the last year - I recall that you needed to pass always both inclusion and exclusion columns to make it work with flow variables…