Since your alignment is correct and nothing has changed between cuts, the laser, mirrors and lens remain aligned so unlikely to be the issue.
Laser divergence over that distance is very unlikely unless the laser bay is full of smoke power loss will be negligible consequently power should not be an issue.
Have you looked at the air flow of the air assist at each location of cut, a greater pressure can cause more material to be vaporised increasing Kerf.
It’s not unknown for material to have different Kerfs, even within the same sheet, have you tried turning the sheet around 180° and trying the same cut?
Yes thats MDF. That sample burn was with zero air assist. Im literally trying to see what the thinnest line I can get is to make sure Im in focus so that was a 13% power burn with 0 air and at 20mm/sec it’s definitely not the material. I cut hundreds of these a month and it’s consistently thicker kerf in that top corner.
Doesnt seem to matter if Im at low or high power either. Kerf is always thicker