Before you replace the membranes, replace both the sediment and carbon filters. While they are apart, clean out all the gaskets and housings with fresh water.
We use micron 5 sediment filters, but would imagine micron 1 filters would clogg without much visibility of filtered particles. One of the local cleaners had a slow water flow and replacing both these elements and cleaning everything out rectified the situation.
it said he has new prefilter on original post, although thats great dvice for people having this problem and have not yet changed the pre filters as this is the main coause of the problem, second is air getting into the system (this does not have to make a leak, it can suck air in and not let it out very few thingsto check to correct.
I would want to know the flow of water, as the water company could have restricted it.
in my area some days it will fly out alot more some days seems a little slow this is them controling the water (if there is a leak somethere they drop the pressure, for other reasons they restrict the flow this does impact more so if you are anywhere near the end of the line on your water inlet to your house.