where is your pump is it before or after you prefilters.
if its after you probably need new prefilters, if its before check your water flow/pressure.
my RO wont come on if the water flow/pressure is too low.
it sounds like something is plumbed wrong to be that high.
you probably have already. but check all the pipes again.
can you check each membrane output seperatly. see if they are working as individuals.