I updated to 1.18.7.2438, which specifically mentions “(Transcoder) Hardware encoding on older Intel processors could produce very low-quality output in some cases. (#10863)”
However unfortunately the problem still exists for me and doesn’t seem to be improved at all.
These issues came when Plex upgraded their transcoder w/ PMS on v1.18 version. Prior to the 1.18 versions, there were no transcoding issues w/ intel hardware acceleration.