Losing Flow in the system

I have a single vane pump connected to a 3-position-4-way directional control valve (with relief), then to a pressure comp flow control valve at the pressure port regulated at a supposedly constant flow rate then to an outside system with its control and relief, ultimately to a set of cylinders before returning.
When various functions are engaged in the cab's control, ie joystick, we notice a variable drop in the flow leading the cylinders to slow down. This does not happen to every joystick function, only a few.
Can someone explain if it's possible to have variable flow in my setup? How? The flow characteristics of the pressure comp flow control valve is flat. I don't understand where I'm losing flow to. Can it be heat related? If so where can my back pressure build up? Thanks in advance

A scale drawing of the piping layout would help.

Are ALL of the pipes sized for efficient flow at the pressure and rates you require?

On the operations where the problems exist, is the volume demand greater than the ones that work OK?

Variable flow might be possible with feedback to the pump motor speed controller, but I would be surprised if that is what s needed.

It seems to me it might be a flow-volume thing, but without knowing more o the system, it is hard to say.

Dave
Generally, I will not give you the answer to your question, but I *will* guide you into discovering how to solve this yourself.