Need Help! Problem with cutting out angeled pocket

So I made a file on solid works for a les paul guitar, and the neck pocket needs to be at an exact angle for the guitar to work good. I have this angle in the solidworks file, but for some reason the cnc router (using Partworks 3D) I use doesn't consistently cut out this pocket correctly. A couple of days ago I tried it with a .25 inch bit with a plunge rate of .25, and that worked . The next day all I changed was the plunge rate to .125 and it didn't work. it cut out the profile of the pocket but half of it was at ~.125 inches the the other half was at~.25 inches with no angle.

I was wondering if anyone had any ideas to why this is happening because I am completely stumped.

Thanks