The most common cause of a pressure increasing, beyond what is necessary, is a leak in the system/mask. It may be a leak in the connections to the mask, or the hose. Please check to make sure these connections fit tightly.
Another reason is an excessive leak at the mask. Please make sure you have a proper seal between the mask and your face.
Check the connection of the tube adapter and the outlet tube (the rubber piece where the tube adapter connects to the machine). If the tube adapter is not properly seated in the outlet tube, the pressure sensor may not be getting the information it needs to regulate the pressure. Also check to make sure your outlet tube is not torn. If it is torn, the device will need to be returned to be repaired.
The last reason could be the Z1 may be sensing an obstruction, which reads as an apnea, and thus increasing the pressure. This could be caused by congestion, or a mask system that has very low flow rate. If you have a mask with very low flow rate, such as some of the very small nasal pillow masks, you may want to try a mask with less restriction such as a nasal mask. If none of the above are successful, please contact the provider you purchased your Z1 from.