Check three things:

1. Which view were you in? With several kitchens, the header Kitchen dropdown decides whether you edited Global View or a specific kitchen. A kitchen override only applies to that kitchen; Global applies to every kitchen that has no override.
2. Is the setting overridable? Most settings are global-only and are hidden while a kitchen is selected; if you can see and edit it while a kitchen is selected, it is overridable.
3. Is the customer on that kitchen? Customer-facing pages use the kitchen the shopper has chosen; a change to Kitchen B is invisible to shoppers browsing Kitchen A.

Remember also that a blank value saved for a kitchen is still a saved value — it does not fall back to Global.