Okay, I managed to setup the encoding the same way you did:
One thing I noticed, which is probably not related is that you are using 'baseline' profile. May I ask: Why? (It's ages since I saw someone using it, which is why I'm curious. 
)
1st result: It crashed with:
(so around the same position)
-> testing more
Cu Selur
mencoder -lavdopts threads=8 -really-quiet -subcp UTF-8 -sub "E:\Output\ONEPUN~1.ASS" -sid 6 -ass -of rawvideo -o - -ovc raw -noskip -vf scale,format=i420,scale=1280:720,ass,scale,format=i420 -sws 10 -nosound -mc 0 "C:\Users\Selur\Desktop\One Punch Man S01E07.mkv" | x264 --preset slower --profile baseline --level 3.1 --ref 5 --sync-lookahead 48 --partitions i4x4,p4x4,p8x8,b8x8 --vbv-maxrate 42000 --vbv-bufsize 14000 --sar 1:1 --non-deterministic --range tv --colormatrix bt709 --demuxer raw --input-res 1280x720 --input-csp i420 --input-range tv --input-depth 8 --fps 24000/1001 --output-depth 8 --output "E:\Temp\2022-04-11@16_35_20_0910_02.264" -)1st result: It crashed with:
x264 output: 26542 frames: 103.91 fps, 1511.37 kb/s
exitCode: -1073741819 and exitStatus: 1-> testing more
Cu Selur
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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.