The tray may not be seated on the supports intended for it, or the rail arrangement may need assessment. Do not balance a loaded hot tray on an uncertain fit.
What the observation means
Extendable rails and ordinary wire shelves can use different locating points. Mixing accessories from another model can appear workable while leaving the tray insecure. A rail that binds or feels loose should not be forced.
A useful next step
Allow everything to cool, then compare the owner-accessible arrangement with the manual. Use only compatible supports and accessories. If secure seating cannot be confirmed without dismantling, leave that shelf unused and describe the affected side and tray type when arranging assistance.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.