Sculpfun S9 loses focus/power when cutting on left side of the MDF board

My Sculpfun S9 seems to lose focus/power when cutting on the left side of the MDF board.
Cuts made on the right side of the mdf board are perfect, while those made on the left side of the board cannot cut the board, using the same parameters.
Has anyone had this problem?

Make sure the board is level. Either the board is warped or your surface that the board is on is not square to your laser head.