I do have a vacuum but maybe it's not working well enough in that direction of cut. I'll have a closer look tomorrow and also try another bit.

This needs much more than 1200grit, even with 150grit it takes a bit of work to remove the recess where the rough part is!

How much of a finishing pass do you chaps recommend for acrylic? I was using 0.3mm but maybe if I used more, it would sort it out?