Issue with fillet machinning using mach3 and fusion

Hello
I run small wood job on CNC.
I just got a new CNC which is controlled with MACH3.
I was used to run a GRBL controlled CNC (Shapeoko)

I post processed an existing cam i already runned on my shapeoko with the mach3mill post processor.
everything was ok until i had to machin fillets.

The fillets are not on the good place, like if flat part of my tool were ignored.
I had no problem on my shapeoko with the same toolpathes.
it is a 2D contour toolpath with fillet bit.
anyone has a clue ?
you can see différences fusion VS reality in the attached photos.
thank you
Remi

after verification i noticed that the tool tip diameter of my roundover bit changed by himself for unknown reason.

all is fine with good setting.

thank you