AI + Multiplayer + Limited by Mainthread

Running a reasonable spec PC and started getting some CTD - sometimes during the load up other times during early part of Flight - but usually with a complex airport or aircraft…

Noticed from the in game FPS counter was getting alot of red and “limited by MainThread” error message although FPS usually remained 20-35fps…

Tried to optimize my graphic settings and importantly disabled the multiplayer and set to AI traffic only (setting to c20%) - this seemed to improve things dramatically was able to fly over london with no crash for a good 40 minutes…however strangely despite having AI on (set to 20%) did not see any aircraft at all?
Anyone any ideas why this would reduce my CTD and why I am not seeing any AI aricraft? (note have a good internet connection (have cache set to off) and a 2080ti GPU…)