Pilot reported engine roughness from a suspected fuel line blockage at cruise. Pilot elected to diverted; refueled and continued to destination.

Narrative

I was flying my experimental airplane (Aircraft X) from my home airport of ZZZ to ZZZ1 on the morning of Day 0. I was about half way into the flight (1.9 hours) cruising at 5;500 feet MSL. I was using Flight Following and passing near ZZZ2 when my EFIS gave me an indication that I was losing fuel pressure and my engine began to lose RPMs. My engine is a UL Power 350is and was running well before this happened. When the engine began acting up; I decided to land to diagnose the problem. I immediately called Approach and notified them of the problem and they cleared me to land at ZZZ2. Since I was over the airport and at 5;500 feet MSL I had ample time to trouble shoot and prepare for landing. I landed uneventfully and taxied to the ramp to effect repairs. In fact; as I was on final my fuel pressure came back and I had full control of the aircraft. My fuel system is designed with two 15-gallon wing tanks that gravity feed to a 1.75-gallon header tank located aft of the cabin. Each of the wing tanks has a cut off which I use to manage fuel balance in flight. About 20 minutes prior to the problem; I had switched fuel tanks and I suspect that some type of obstruction or possibly vacuum was created that was not allowing full flow of fuel from the right-wing tank to the header tank. It was not a complete obstruction as the fuel tank had used about 3 gallons of the 15 it contains. After landing I did some trouble shooting refueled both tanks and continued to my destination (after orbiting the airport) without further incident. During the remainder of my flight; I left both fuel tanks on and the fuel flow appears to have been fine. My total fuel onboard the plane at the time of the incident was about 20 gallons of the 31.75 it holds. When I refueled at ZZZ2 the suspect tank took 3.5 gallons and the other tank took 8 gallons. When I reached my destination I drained the tanks; inspected the filters and checked the fuel for contamination all was good. Bottom line is I suspect a partial obstruction did not allow the fuel to flow into the header tank which slowly depleted and reduced the amount of fuel flowing to the engine. I have flown the aircraft for another 5 hours since this happened without incident.