Poor Patrick. I'm asking the team - I know I've seen this fixed before.
You could also File > Export > PNG Sequence and WAV, and then use After Effects or Premiere to bring it together. See 43:30 here:
Dave forwarded this and I'd originally thought it seemed like this AME issue: Re: CA export via Media Encoder -- can't get to work. PLS HELP!
The fix in that case is to choose a width (in Character Animator) that's a multiple of 16, but above it looks like you're still seeing the issue when the width is set to 1920, so maybe there's something else going on (or I'm misremembering the precise details). I think there was also an issue in Preview 4 where AME has to be relaunched for a width change in Character Animator to take effect, so maybe there's an issue there.
Hopefully that helps.
I changed the fit to scale to fill to scale and it now export properly.