Match the stopper to the exact disposer model and the manufacturer's approved part reference. A batch-feed stopper can be part of the operating control, so fitting the sink opening is not sufficient evidence of compatibility.
What the observation tells you
Two similar-looking stoppers may have different operating positions or activation arrangements. A generic drain plug can hold water without controlling the appliance correctly. Do not modify, weight or force one to make it activate.
A useful next step
Retain the old stopper or clear photographs and confirm the replacement before ordering. Keep the disposer unused if its proper control stopper is missing or damaged.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.