When the servers went down a week or two ago, the connection difficulties most all had for about 24h, after they fixed this I was back to great performance, stutter-free.  About 48h ago now this changed and what starts out fine by the time I'm taking off we go from an unlocked rate of 50fps down to 20-30 fps, and don't see main thread nor GPU nor VRAM being stressed at all.  Near as I can recall no changes to the sim.  This is with both PMDG 738 and FBW 320nx out of 3 different airports that typically don't drop frame rate significantly.  And this is with FSLTL on or off, so that's not at play here.  

Anyone relate to this recently?

 I have had this happen and posted about MSFS losing focus despite being full screen and in the foreground.  It is quite obvious if you mute on loss of focus but my first clue is my view presets no longer work and my mouse cursor looks different. 

If I simply click on the MSFS window it almost flashes back to foreground and FSPS and functionality resume.  Do you also have GSX? 

Thanks, yes I have GSX and this occurs after GSX has closed itself after pushback.  I'm hyperaware of MSFS losing focus if I click on my 2nd screen but as I don't use NV DLSS FG it's not significant at all, barely impacts performance, unlike when FG is enabled.

I am now at cruise from KLAS to CYVR and performance is about as typical.  For some reason these metro areas are now killing performance and this is new to me, completely new.   I suppose my next step is to try bypassing the community folder entries completely.  Or my other knee-jerk intervention:  clean out the DX caches and update the GPU driver w/ a clean install.  I have to think if it's server-side others would be reporting on this.

Not that anyone's listening but the culprit for the past 72h now was completely resolved by turning off photogrammetry and deleting and stopping the Rolling Cache.  Not sure which did it bit very thankful we're back to normal again.