.....It might not be a fault, it might be low pressure.
The dynamic pressure at the shower will be lower when the kitchen sink cold tap is turned on, and if the pressure is normally marginal, this could cause the lp fault. Try and plot what times of day the "random" lp faults occur. Could be at times of peak demand when pressure is lower generally as more people are using water.
...try checking the shower head for blockages and clean out also the hose to outlet . you could also check the plastic tube that leads into the pressure switch in
shower unit for blockages
did you clean the small pipe that leads to the pressure switch as well ,