So I was able to run sap through each individual housing today and sure enough, number 2 of 5 was passing sugar. It was showing 3 brix with all the 4 of the others at 0. I bypassed that one and ran the rest of my sap through the other 4. Tomorrow will be warm so I don't expect to get a run and I wanted to boil everything off today.
Right now I have 90 gallons of permeate at 1 brix. When I run it through the 4 menbranes I get 2.5 brix so I'm running that back to my holding tank. Tomorrow I'll use it to figure out what's wrong with number 2.
Thanks everyone for the great advice here. I'm feeling much more confident that this system can make a big difference.