Weird that now when I have "Loop section" active, the volume is lower. Turn off "Loop section", volume goes back to normal.
I would say about 3 to 6 db change.
I think it is only on one project, just test another project and it is fine.
But what could it be about this project that causes lower volume if I "Loop section"?

It sounds like there might be an automation event(s) in that section. Have you checked for that?