DIAGNOSIS The roller guide or hub underneath the glass plate is dirty with grease/food debris or is cracked/worn, creating drag.
FIX Remove the glass tray and the underlying plastic ring (the hub). Wash both in warm soapy water. Scrub the three plastic rollers on the floor of the oven cavity and the inside of the ring where it sits on them. Dry everything completely before reassembling. This solves 90% of cases.
IF THAT DIDN'T WORK Inspect the white plastic hub for cracks, especially the center hole or the tabs that hold the glass tray. A cracked hub wobbles and binds. You need a replacement hub (part #ES352395).
HEADS UP Never operate the microwave without the glass tray and hub installed. It directs heating and protects the waveguide cover. Running it empty can also damage the magnetron.