I know two people who are having this problem. One has a Mosquito and the other has a Flying Squirrel (which is a pretty cool little yo-yo).
The problem they are having is that their stings are slipping off their bearings and getting stuck between the bearing and the spacer.
Their spacers are put in correctly. The yo-yos are snug but not over tightened. New string or old string it doesn’t seem to matter, it still slips off.
Has anyone had this problem and do you know how to fix it?