Drastic colour + exposure shift when exporting with MPEG audio instead of ACC | H.264 - PPro Beta M1

When exporting my last project with ACC audio, the audio sounded terrible (tinny and flat). Changed the audio settings to MPEG instead and the sound came out perfectly, BUT for some reason there is a very noticable colour and exposure difference in the export.

I have done multiple exports with different H.264 configs, all with the gamma correction LUT, but the only thing that makes the colours and exposure change is when I switch the the MPEG audio option. Both problems go away when I export to ProRess, but the file sizes are huge and not supported by some platforms.

Anybody know why this is happening? Is it maybe just a Beta Bug? Cheers