The needle is returning to the wrong position.
Check needle position buttons
Ensure that the needle position is set to be needle up and not needle down.
Check index counts
Check if index counts are counting in Folder -> Diagonistics -> Motor Index button. Turn the handwheel by hand and see if index flag is updating. Make sure the belt is connected as the motor needs to turn as well.
If there are multiple Index Counts per revolution:
The index disk is probably oblong and is toggling the index in the wrong position.
If there are multiple index counts per motor-powered revolution and normal index counts when turned by hand:
Check the earth ground connection to the casting. If it is not connected it will give many index counts when the motor EMF interferes with the PCB.
Ensure that the index is set correctly inside machine and the flag is being engaged in the index channel.
Ensure that the index flag is not spinning freely on shaft.
Ensure that the motor pulley is not spinning on the motor shaft.