Smeg A-42 Wok Burner burns but not to full capacity

Our cooker has a wok burner ring. It lights fine, but doesn’t seem to burn at full capacity. The circle of inner gas flames – only about half of them fire up, and are intermittent. Even the outer ring of flames seems to not burn up as high as they used to. My completely uneducated guess is it is like there is not enough gas pressure for that ring to burn correctly. All the other rings are fine. We are running on Propane and the correct nozzles(?) were fitted when it was installed. It has been like this for years, only now getting around to researching it! Any advice?