Membrane degradation? Normal use is 3-5 years. This filter can only withstand 4 bar max. Add a sediment pre-filter such as the Secure water filter which is back washable by a twist of the filter body. Bro weikee uses that for his mother's house. Search this thread for aeiuo228's post. You can still have the membrane optionally after the Secure water filter.  This way it doesn't have to deal with sediments which should reduce biofouling and should lasts 7 years. The other way is to move the membrane after tangki and water pump but have to ensure pressure cannot exceed 3.5bar and if it bursts measure, must be in place such the it had a safe place to leak to without causing a flood on the roof.

Water pressure gauge affixed to the piping before or after or both sides will indicate the pressure on those side installed. Most pasang after but there are those who insist will pasang 2 sides but rare.

The gauges will measure in Bar, Psi, k/MPa depending but just memorize the rates will do:
1bar = 100kPa = 0.1MPa or approximately 14.503775psi.

Most likely the membrane is worn out. Normally it's recommended to change  after reaching 5 years. To protect its service life, the filter like I mentioned earlier would be used as it's pre filter. But because others find the water clean enough at 1 micron, they find it that it's good enough. If you prefer it cleaner (I would) 0.01 micron is still ok for what it protects e.g. shower heads, tap aerator, washing machine, water pump, solar heater, drinking water filter, etc.

To ensure that the pressure do not exceed say a predefined threshold say 4 bar, you can pasang what's called a pressure reducer valve. Some pressure limiter /reducing valves can set between 2.0-4.5bar depending upon application. Solar water heaters or centralised water heaters in their manual will say not to exceed a certain limit and that's where they are installed usually at their inlet side. Some models also come with water pressure gauge affixed.

Also, if your home is near the water utility pump house, like just downstream of it, expect stronger pressure.

Match gauges and valves according to inlet piping diameter which usually is about 3/4" (DIN 20) nominal plumbing thread (NPT) size. Your plumber can advise what's to be used for your installation's case.

Also, I would advise that the piping (from meter to filter and filter to indoor after meter) to use HDPE rather than PVC. HDPE has higher thermal stability. PVC softens in excess of 45°C. If you can shade the filter area, all the better.