When Pro-Stitcher runs a design, it does something you'd normally do with your hands: it presses the buttons on the handlebars. Start, stop, needle up and needle down all come from the tablet. On Avante and Fusion machines (including similar OEM machines), those commands take a route most owners never see.
The Pro-Stitcher wires run down to a small Handi Quilter board mounted on the Y-encoder, on the carriage under the machine. There they plug onto the board through a small black connector with a latch. The board moves the signal onto spare wires in the encoder's ribbon cable. That cable is already connected to the machine's control board at its other end. It's a tidy design because no extra cable has to run to the machine head. The weak point is that little black connector.
With the cover on, you can only see the top of the connector. It looks fine.
With the encoder cover on, you can only see the top of the connector through the opening, and everything looks normal.
Cover off: bare pins show under the connector. It has lifted off the board.
Take the cover off and you may find the connector has been pulled up the pins. The wires are still attached, the plug is still sitting over the header, and nothing looks broken. Look just below the plug, though, and you'll see bare pins where it should be pressed flat against the board. The plug looks connected, but the circuit isn't.
Reseated: the connector sits flat on the board with no pins showing.
If the connector was seated and the problem is still there, the next places to look are the encoder cable and its connection at the control board. Both take more work to reach. MOTT members can bring this to a Saturday session or a support call. Everyone else can call the shop and we'll walk you through it.