Hi in most cases the cause is simply a dirty sensor.
You need to clean this sensor . Blow it out with a blower brush or air can.
Let me know if that works, you need to do this with the unit unplugged from power!
Please rate kindly I will still be locked in with you until your problem is solved;-)
its called the Foc sensor
Also it could be -2nd transfer roller separation.Clean using vacuum cleaner the transfer unit and the electrical contacts.
Its petty easy for a tech lol.
Your very welcome!
Please rate kindly!
Once you rate, if you need me further I will still be here for you no additional cost!
Thanks again Lisa!