Hi!
I'm having trouble picturing how your panels are connected. Can you make a diagram or post a pic(s) to help visualizing it?
One thing I do differently from you is my panels, once split, stay split and each has its own return to the pool.
I do know that sometimes the built in valve on the roll-able panels can be confusing and you may need to re-plumb the panels so the entrance is at one corner and the exit at the other, with a new valve at the input and leave the built in valve open.

Carl