I assume that the OP does not have a manometer (sight glass) that reads the pressure at the bottom of the grain bed. As a RIMS user for almost 15 years, I can assure readers that it is very important to monitor and adjust the flow rate through the bed to avoid excessive head loss through the bed. If a user tries to pump at a pump’s full flow rate, it is possible to create a very strong hydraulic force that can ‘compact’ the grain bed. In essence, the bed is compressed to the point that the voids between grain particles collapse and there is nowhere for the wort to pass.
Without a manometer ported into the bottom of the grain bed, a user would have no idea that they are over-pumping the bed and creating that excessive hydraulic force.
The permeability of the grain bed does change during the course of a mash. It is initially relatively low and I have to significantly throttle the pump to avoid compacting the bed. As the extraction and conversion progresses in the mash, the permeability improves and I can open up the throttling valve. I never have stuck mashes.
The other thing that a RIMS user HAS to include in their system is a PID so that the wort is not overheated. If the wort is overheated at ANY time while passing through the circuit, that will quickly denature the enzymes. You will end up with starchy wort that does not convert. Be sure that the temperature sensor for the PID is located immediately downstream of the wort heating point so that the PID can better avoid that overheating problem. The temperature of the wort matters more than the temperature of the mash bed. Don’t overheat the wort in pursuit of producing a certain mash bed temperature.