If your printer is skipping or feeding extra/blank tickets you first want to make sure your tickets are inserted correctly into the printer. Although you may have done this for many time in the past we like to ask you review the following documentation: Ticket load procedure or view this video: https://www.youtube.com/watch?v=lWBIUzwlh2o
When your tickets are inserted correctly, you may need to setup the width of the paper guide (slider setup). Please turn off the printer and check the setup of your ticket slider, the ticket should not be able to move more than 1mm sideways. Please review the following documentation for the specific setup in your printer: Paper guide ticket width adjustment (ADJ2, ADJW, ADJ4, RADJW & RADJ4) or Paper guide ticket width adjustment (UPG)
Once you have setup/checked your slider setting, power the printer back on and print a few ticket to see if the problem was solved.
If the problem still persists then move forward with cleaning the optical sensor (opto) in your printer. The cleaning instructions can be found here: Cleaning the optical sensor (opto) on a Lemur or view this video: https://www.youtube.com/watch?v=AtdQecP2uTs