YouTube just finished processing my video to 4K here:  I tested on 3 PCs 7700K 1080FE SSDs (2160p @ 60Hz capped to 29.5 via NI)
8700K 1080Ti  SSDs (1440p @ 60Hz capped to 29.5 via NI)
7900X TitanXP  SSDs (2160p @ 30Hz) Results were the same on all computers.  Summary: 1.  TFR = Unlimited with high graphics settings will increase the probability of stopping Autogen batches from rendering
2.  TFR = xx frames with lower FFTF values (below 0.33) will increase the probability of stopping Autogen batches from rendering
3.  The TFR = Unlimited issue is NOT specific to any add-on and can be repeated in a default P3D V4.3 and P3D V4.2
4.  If the Autogen system gets far enough behind on rendering it stops rendering completely (pause will not recover processing) and will require a scenery reload (map a controller button to it). Graphics settings are dotted thru-out the video.  When add-ons were used (final last test towards end of video from LFLI - EGLL complete flight) I was running TFR=31, FFTF = 0.33, Vsync ON ... Add-on list was extensive (Orbx FTX Global, Orbx OpenLC EU, Orbx HD Trees, Orbx Vector, HiFi AS4, Turbulent Flora, FSDT LSGG Geneva, LLH Creations LFLI, ChasePlan, PILOT's NG 2018 Mesh, FSFX Packages, UTLive, ENVTEX/ENVSHADE, and a few others). I kept the flight test between 0 - 7000 ft and speed of 400-500Kts and heading the same direction (about 333).  GA aircraft tend to fly slower so they will put less stress on the Autogen batch system ... so experiment (Unlimited with Vsync make work sufficiently for low and slow flights, and/or lower FFTF values if using TFR = xx). I have NOT tested with the FSPS Dynamic FFTF product, I have purchased but not had time to try it yet. I have made LM aware, but it's most likely an "expected" result and who knows what the future might bring. Cheers, Rob.