What are your flows rates?
Does your concentrate flow decrease as you close the concentrate needle valve? Permeate flow should rise slowly as you raise the pressure
Where is your pressure gauge plumbed into the system. Before the membrane inlet or after? Usually there is a little bit of pressure loss through the membrane.
I found the best location to put high pressure gauge was before the membrane. Gave me the most accurate pressure rating. Some ROs have them before and after to show pressure loss through membrane.
Check your procon and see if it has the nut on the side for pressure adjustment. It might be one that has relief so double check that.
If you can't get over 150 PSI with water then you aren't going to get much higher with sap. I can get up to 250 on permeate if I want to. So something is going on my guess is your procon is set up with relief or the pressure screw needs to be adjusted.
You don't want to have a full tank of sap and be screwing with the RO to try and get it working and waiting for parts etc
600 taps on vacuum
Lapierre mechanical Releaser
CDL electric releaser
2.5 x 10 CDL Venturi ( new for the 2024 season )
Home made modulating auto draw off
Homemade RO 2 x 4" membranes
CDL 16 x 16 bottler
Wesfab 7" filter press
Delaval 73 vacuum pumps
12 hives of bees