It is odd that it happens AFTER each corner and at teh same point in the next LINE, and it is happening in both axis. That looks mechanic and looks like flex OR axis shift(slipping coupler, belt stretch) in both axis. The main indicator is it gets worse with higher speeds . That is when cutting forces grow higher.
Try the sequence in Exact stop mode (G61) OR reverse the direction of the cutting and see IF the shape of the problem changes.
Does the toolpath LOOK correct in Mach3 ?
(;-) TP
(;-) TP