Render bug with PNGs (16.2.8.005 Studio/17.1.1 Studio)

We're getting artefacts in Resolve 16.2.8.005 Studio and 17.1.1 Build 9 Studio render output for a track with PNG subtitles: composite mode normal, zoomed and positioned.

Playback in Resolve/timeline is fine.

See phone cam clips (playback in timeline vs. render with artefacts) and actual PNGs used at
https://www.filemail.com/d/ayvbtcykbgpzozi.
Sorry for potato quality of the clips but I am still in shock.

The PNGs attached were generated with Subtitle Edit 3.5.17

DE-2997fps-DVD-air-Null_Sonne_No_Point0023.png (84.29 KiB) Viewed 654 times

Screenshot - Resolve 17 render bug in media viewer.png (616.13 KiB) Viewed 654 times

Even weirder artefacts in Resolve 17.1.1 Build 9 Studio:

Same project, some PNGs (subtitles) will randomly render yellow and fringed in the media viewer.

See attached screenshot of a subtitle PNG overlay with artefacts in media viewer and the original PNG file.

Screenshot - Resolve 17 rendered file with artefacts.png (234.29 KiB) Viewed 651 times

This ended up in the rendered file.

Any other information required to get someone to look at this issue? tia