***UPDATE***
I have resolved this issue today!
for a while I thought I had an issue with my OMAS cutter block, even took it to a machinist to check, the machinist commented maybe it is the sliding table?
I was getting the same issue with another cutter block recently, so I wondered if it was something else, maybe my setup? maybe the sliding table?
I had to do 100 x tenon cut recently. so I finally investigated this today and played around with the spindle moulder.
I know it will create burn mark past mid point, I thought to myself. MAYBE, just MAYBE, the tilt of the spindle is not dead on 90 deg. although it is reading "0" on the screen?
I started with + and - 0.1 degrees on the spindle. no improvement, then + 0.2 deg. slight improvement!!
I cranked it up to + 1 deg. it was creating burnt marks on the other side, so I adjusted back to + 0.9 deg... and EUREKA!!!!
Below is the video I took today. no more burn marks and the cut was square!
https://www.youtube.com/shorts/uespGfV0l7M
a few months ago I did move the machine and the move could have affected the calibration? the tilt was showing a funny number after the move and I thought I zero'ed it but it seems I didnt zero it properly.