I agree with @greg.obj. Your machine is trying to go from horizontal at 300 ipm to vertical at 200 ipm and needs to know to slow down ahead of time. [Edit: looks like I misunderstood which direction it was moving.] There are acceleration limits, so if it doesn’t start early enough, it won’t be able to stay on the toolpath, and then it’s overconstrained and fails in some way. Enabling smoothing will allow Mach4 to look farther ahead and adjust earlier. If you’ve reduced your motor acceleration parameters, you can try setting them back to default values, if only to help with the diagnosis.
Here’s a video from Avid that discusses the topic.
