You need to hunt down the problem step by step.
Start by disconnecting the pipe coming out of the three pre-filters to see if they are the problem. If they are then one at a time remove the pre-filters from the housing, leaving the other two in, you will soon be able to isolate which is blocking the water flow. It is not unheard of for new pre-filters to block a system.
If it is not them then isolate each membrane at a time time. Finally dis-connect the pipe going into the final DI stage to see if that is the problem.
If you go through the unit systematically you will find the problem but it may take you an hour to do.