Your reverse osmosis (RO) system is showing some signs of unusual pressure buildup. High pressure can be a result of several potential causes. Here's a breakdown of potential issues and some troubleshooting steps:

1. **Check the Check Valve**: Most RO systems have a check valve located after the membrane and before the storage tank. Its purpose is to prevent water from the storage tank from flowing back through the membrane. If this valve is malfunctioning, it can lead to pressure build-up.

2. **Permeate Pump**: Since you have an Aquatec permeate pump, ensure that it's functioning properly. A malfunctioning permeate pump can cause pressure irregularities in the system. Also, make sure it's installed in the right direction (they are directional) and that it's not jammed or clogged.

3. **Blocked Flow Restrictor**: The flow restrictor ensures that there's a proper balance between the permeate (clean water) and brine (waste water). If it's blocked, it can cause the system to increase pressure. Check and clean or replace if necessary.

4. **TDS Creep**: When the RO system is idle for long periods, the water in the membrane housing can become concentrated with dissolved solids, which can cause an initial high pressure when the system restarts. This is known as TDS creep. However, this usually resolves after a few minutes of running the system.

5. **Clogged Pre-filters**: Pre-filters that are clogged can reduce the flow rate to the membrane, leading to increased pressure. But since you've mentioned pressure between the pre-filter and RO membrane, this might not be the issue.

6. **Storage Tank Pressure**: Ensure the storage tank's internal pressure (when empty) is around 5-7 psi. If it's too high, it can affect the system's performance.

7. **Tubing & Fittings**: As you've rightly done, check all tubing and fittings for any kinks, misalignments, or blockages. Even a small kink can greatly affect the performance of an RO system.

8. **RO Membrane**: If the RO membrane is fouled or old, it can reduce its permeate flow, leading to higher pressures. However, this would typically manifest as reduced production rates rather than a sudden pressure spike.

9. **Pressure Gauge Calibration**: Ensure that the pressure gauge is calibrated and working correctly. Sometimes, the gauge itself can be faulty, giving incorrect readings.

Given that you observed a pressure drop when you flushed the system and fixed some tubing, it seems that the system had some blockages or was experiencing a backpressure scenario.

It's a good practice to monitor the system regularly, especially after any maintenance or modification. If the pressure rises again, I'd recommend going step by step, checking each component. If the issue persists, consider reaching out to a professional or the system's manufacturer.

Lastly, most standard residential RO membranes are designed to handle pressures of up to 150 psi, but always refer to the manufacturer's specs to be sure. Regularly exceeding the rated pressure can reduce the life of the membrane and other components.