I don’t know specifically for OpenPype / AYON, but we always ran into color troubles when trying to do a direct encoding from EXR (srgb_linear, acescg or other) to video via ffmpeg.
What have been doing for quite sometime with success is to convert the EXRs to high quality jpg using oiio as post render task (5s extra processing on 10min to 5h tasks is negligible) and then encode movie from the jpg !
EDIT: ah damn, that was a draft meant to be send 4 months ago, sorry of the post digging 