have to look at mine tomorrow, but I think once the tray is on it should hit a stop when you pull it towards you, the wheel shouldn't come of the rail
When I have first 2 wheels on, it glides OK. Wouldn't be able to slide it up to cut point thou without 3rd wheel on. Once 3rd wheel on, and able to push up to cut point, this is when it needs pushed with slight force rather than glides. Defo something up!
Can you check yours to see when putting tray on, and when it comes to putting 3rd wheel on rail, does yours line up perfectly or like mine in the pic!