Do you use the extended work coordinate system in Fusion360? This means you use the fixture table for setting vise or workholding posiions. Currently Fusion 360 has a bug that will prevent you from properly using this system unless you edit the post processor file. It's easy to do and you can follow the directions in my video and fix this issue.
Currently, when you get to G59 the next step from Fusion360 is G59 P1 and you know that the fixure table goes from G59 to G59 P7. Also in Mach4, after G59 you go to G54.1 P1
Someone at Autodesk thought they could save time and generalize this code which actually totally crashed the extended work coordinate system for both Mach3/4
I hope this helps someone...I know not a lot of people use this but for those who do like me, totally shut down their production system with this bug.
Rick

My video- https://youtu.be/El_91Gx5HHk