I've had the exact same type of problem but it was happening in several spots, but it would always happen at that spot. And at those spots - it would "tug" the wrong way, like it would go up/down, or side/side, but would not move diagonally, so I'd get a few stitches of "wrong" and then it would move correctly again. A real drag when you are dong a tight stipple. And it started getting worse, more spots being "bad"
I had this problem with Grace frame, and it was because the rails were not completely parallel. Don't know how they got that way, but I loosened the rails and then used the procedure as for the original setup, and retightened them and it took care of the problem.
I had thought it might be dirt or something sticking, but it was because the machine was getting a bit wonky on the tracks, and then would "slip" to get back straight until it got off enough that it would do it again. Once I reset the rails, the problem went away completely.