Exporting After Effects project in Media Encoder with LUT causes down-resing/pixelation

So I recently replaced my laptop with a new M1 Max Macbook Pro, and since then, whenever I render an AE comp with ME with a LUT applied, it downreses the output. Even in the preview window it shows pixelation.  This workflow works perfectly fine still on my iMac (which is where I've now been using for rendering these as a temp solution). Hoping someone else has encountered this and found a solution?  Screen grabs attached (hopefully they're large enough that you can see the difference.) 

I'm on a 14" MBP M1 Max

OS: 12.1 Monterey

AE: 18.4.1

ME: 154.1

LUT: Gamma correction LUT for h264 from Adobe but this problem persists with any other lut from the menu

It also doens't seem to matter if I choose hardware or software encoding.