Tricky one this. You say the coil pack was changed ,this have 3 coil over plug devices ,one for each cylinder. There is no external fuel filter on these ,It's a sealed for life type fitted in the tank. The fault should still be recorded in the engine ecu memory, so any one with a code reader should be able to access this.

We had a Volvo that once had an intermittent fault of being fine for a while and then would drop to three cylinders. Turned out to be a duff plug lead.

He changed the coil pack and plugs last year so I've sort of rulled them out

Myself I'd be looking at the last thing changed. There are some poor quality coilpacks available. I'd start there and (re)replace these. Any codes logged?

A fuel filter issue unlikely to cause a drop out of just one cylinder.

If it drops a cylinder again try not to run for long as the offending cylinder will be sending un burnt fuel towards the catalyst/exhaust.

Edited by Big John on 27/02/2022 at 22:12