We have the same water
maker, now 17 years old. Our previous owner disconnected the control panel
and we only use it for on/off switch and pressure adjustment. The flow meter is also disconnected.
You may have an air leak in the measurement hose - check your hp hose connections and all hoses.
How clean are your membranes? We recently pulled both membranes and gave them a good rinse and soft scrub.
Measure your output via the waste hose: time filling a container for one minute and work
out your output. Or, as we do, monitor
your tank gauge for how quickly it fills. With original membranes, 20 degree C water, clean pre-filter and good battery
voltage we’re getting 55-60 litres per hour.