Hey guys!
Thank you all for your testing and confirmation of the fix. This will be included in the upcoming PMS 1.18.7 release which should land in Plex Pass beta in a week or so.
In the meantime here are updated builds that are based on the imminent 1.18.6 beta release, and include the Intel HW transcoding improvements and fixes.
EDIT: Updated build to 1.18.6.2349-f0bf4dd50 which resolves the issue with images not retaining their transparency information.