Not a lot of answers to this one
I guess that's because everyone is baffled, as I am. If you are sure your water supply is uninterrupted and there is plenty of pressure (90psi is extremely good without a booster pump - are you sure it's right?) the only sensible answer is that there must be a blockage somewhere before the membrane. I have had systems where the carbon block filter has fragmented and carbon pieces have got into the pipework leading to the membrane housing.
All I can suggest is that you take it to bits, make sure there's no foreign matter in the pipes and housings and then re-assemble it. Leave the pipe from the third (carbon) prefilter disconnected from the membrane housing and connect the mains water up to the first (sediment) prefilter. Allow water to flush through the prefilters only, letting it go to waste for about 10-15 minutes. This should remove any loose carbon from the system. Then reconnect the pipe to the membrane housing and hope for the best.
Sorry I can't be more helpful.