Hi again @Gavin_Attard -
I heard back from the devs. There has already been a fix implemented for use of columnar backend for “common” loop ends (for example the standard Loop End).
The Parallel Chunk End has not been adapted yet, and they are aware of the performance issues. Fortunately there is a ticket for it (AP-19971) that is being worked on.
Hope that helps clarify for you!