The first thing I’d suggest is checking your pulley screws. If they’re missing or loose (i.e. not tight and dead-center on the flat), that can allow the shaft to rotate before the pulley does. That will normally cause a blip. Other causes could be low (or high) pots or high (or low) belt tension. The blip itself is an indication of lost steps, you may want to check out this thread if you don’t find loose pulley screws: [Guide] Offset cutting, Lost steps, Positioning errors, etc
Are the two circles on the picture separate cuts?