Post is the same one I have always used in Fusion, I think EMC2/LinuxCNC. When this occurred in the past, one of the things that seemed to trigger it was increasing the feed speed. But in every case, the preview shown on the machine shows the correct path, while the actual path when running deviates from that. It shows up on the screen while running that the actual path is deviating from the preview. So, for example, during a trace operation of a rectangle sketch, where it should be four straight lines with sharp corners... the result is one sharp, square corner at the start/end point, but the other 3 corners have a radius.
SO!! frustrating, because I don't know if its something in Fusion, or something in the machine software. In this case, I had done a few examples of a part(drink coaster/ornament for an annual party) with small changes until I was happy with it.. Then I started tweaking the feeds to get a faster cycle time, and made a few minor changes to the depth of various trace operations. I had cut one or 2 that were good, and then after minor changes to feed, and depth settings, this issue came up. I've tried reverting to the previous settings, to no avail.... aaggghhh In this case, the feed/speed are all the same for an engrave operation, and 2 trace operations, all with the same tool (45* engrave) These 3 operations are all contained in one post. The engrave of lettering is fine, the trace of the perimeter of part to create a chamfered edge is fine, but the trace of a simple line sketch of a flag perimeter and stripes results in one square corner, and 3 with a radius.