Prores export on Mac M1 only 8-bit!?

[Rocketbottle]

Yikes!!

AE 23.1.0

M1 Mac Studio

Just returned to a client project from last fall and saw something I don't remember seeing before. 

Noticed a severe banding problem in a very dark scene.

Compositing Arri Log & Rec.709 sources in 32-bit, ACES color space, export Arri Log.

Looks good on the monitor, but exported Prores file has severe posterization - like the file is an 8-bit. Tried everything I can think of but nothing helps.

Exporting as 16-bit Tiff looks fine. It has to be export encoding because Tiff-sequence that looks OK is again posterised when exported as a Prores.

I fear all my previous deliveries since the last AE update are garbage. Has anyone seen something like this?

Help, Adobe!

[Rocketbottle]

Just saw a discussion about Premiere exports: "... the files are 10-bit, but they get decoded as 8-bit unless I turn off "hardware accelerated decoding". Except I have both "Enable hardware accelerated decoding" and "Enable ProRes hardware accelerated encoding" off.

This is not good. 😡