Looks like the tail of the “r” is cut off. That’s clearly a place where the X motion stopped working correctly. Probably collided with a physical limit.
Also, it looks like the “r” is farther to the right on the acrylic than it is on the cardboard. Thing is, the centers of the letters are even further right. I suspect the head (hardware) was physically further to the right than the software thought when this cut was started.
It looks like the insides of the letters were cut first. They cut correctly, albeit too far to the right. Then when it tried to cut the outsides of the letters it collided with the physical limit on the right. Since they are steppers and there’s no limit switch the machine was none-the-wiser.
It looks like the outsides of the letters started being cut near the tip of the tail of the “r”, which makes the location of the error difficult to spot.
What would make the head hardware be farther to the right than the software thinks?
The head getting knocked.
Bad homing (root cause: no limit switches).
Running into a physical limit on the left with no way of knowing (root cause: no limit switches, usually).
Maybe some kind of belt slippage.
Pulses not being transmitted successfully to the motor drivers. (doubtful)
Bad motion planning. (also doubtful, IMO)