It encodes faster than x265 in some situations with so much space saved

on ffmpeg?
I tested it like 6months to a year ago I think, and it had similar storage requirement at similar visual fidelity but transcoding took what seemed 5x to 10x the time

/e: for future reference, I'm testing a transfer to transcoding to AV1 instead of hevc

ffmpeg -i /path/to/infile -c:v libsvtav1 -preset 9 -svtav1-params tune=0:enable-overlays=1:scd=1:scm=0:fast-decode=1 -crf 50 -g 240 -pix_fmt yuv420p10le /path/to/outfile

These are a mix of what I read here:
https://gist.github.com/BlueSwordM/86dfcb6ab38a93a524472a0cbe4c4100
and here:
https://trac.ffmpeg.org/wiki/Encode/AV1

general gist:
preset is encoding speed, higher is faster, this setting gets me a bit faster than what i had my hevc encode set up
tune=0 tunes for being good looking
fast-decode lessens cpu use on decode
crf 50 seems fine for my use
-g 240 changes keyframe insertion to every 240 frames
-pix_fmt yuv420p10le gives 10bit color depth which helps with dark scenes and doesn'T cost much space

did you delete (or rename, as a backup) you shader cache and/or shader pipeline?
could be that an updste changed something that doesn't play well with old shaders?