Threading costs lots of RAM. 
So if the whole thing get's instable when you use more threads it's probably a memory limit issue.
Avisynth+ how Hybrid uses it, is 32bit only and thus is limited to <4GB RAM usage.
Vapoursynth on the other hand is 64bit and thus not so limited in regards of RAM.
You can use AVSMeter (https://forum.doom9.org/showthread.php?t=174797), simply copy the AVSMeter.exe into your Hybrid/32bit folder and it should work fine and call it inside a Windows Command Prompt.
Disabling 'add distributor()' is an Avisynth MT option, by default Avisynth+ is used so that won't do a thing.
Assuming you got AVSMeter running, try whether it helps if you add:
Cu Selur
Ps.: As side notes:
a. in theory one could use Avisynth filters inside Vapoursynth, problem is there isn't a 64bit version of amDCT so that wouldn't help either.
b. higher cpu usage with Avisynth doesn't necessary have to mean higher speed
c. wondering why FFVideoSource is used for your source, when 'LibavVideoSource instead of FFmpegSource' is enabled.
d. Instead of using FFmpeg as Avisynth Script interpreter, you could also try avs2yuv (by disabling 'Prefer FFmpeg as decoder' and enabling 'Prefer avs2yub to decoder') this might lower the memory usage a tiny bit. (will probably not really fix the issue)
So if the whole thing get's instable when you use more threads it's probably a memory limit issue.
Avisynth+ how Hybrid uses it, is 32bit only and thus is limited to <4GB RAM usage.
Vapoursynth on the other hand is 64bit and thus not so limited in regards of RAM.
You can use AVSMeter (https://forum.doom9.org/showthread.php?t=174797), simply copy the AVSMeter.exe into your Hybrid/32bit folder and it should work fine and call it inside a Windows Command Prompt.
Disabling 'add distributor()' is an Avisynth MT option, by default Avisynth+ is used so that won't do a thing.
Assuming you got AVSMeter running, try whether it helps if you add:
SetMemoryMax(768)Cu Selur
Ps.: As side notes:
a. in theory one could use Avisynth filters inside Vapoursynth, problem is there isn't a 64bit version of amDCT so that wouldn't help either.
b. higher cpu usage with Avisynth doesn't necessary have to mean higher speed
c. wondering why FFVideoSource is used for your source, when 'LibavVideoSource instead of FFmpegSource' is enabled.
d. Instead of using FFmpeg as Avisynth Script interpreter, you could also try avs2yuv (by disabling 'Prefer FFmpeg as decoder' and enabling 'Prefer avs2yub to decoder') this might lower the memory usage a tiny bit. (will probably not really fix the issue)
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Dev versions are in the 'experimental'-folder of my GoogleDrive, which is linked on the download page.
Dev versions are in the 'experimental'-folder of my GoogleDrive, which is linked on the download page.