If you've changed the needle and cleaned, I can't think of why it would be skipping halfway through. Did you hit a glob of glue to throw the timing off maybe? Check the thread path from the spool to make sure you are gong through all the thread guides. Fill and put in a fresh bobbin to see if that helps. Did you leave enough time for the glue to be totally dry? Maybe this side has more glue and it is still tacky?