You have made an extension field ABC hidden in Master Layout via Key User Adaptation, but left the same field available for end user personalization.
One of your end users added this ABC field via Personalization to Advanced Search of the OWL (Object Work List) of an object, but this field is not being considered during the search.
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When you hide an extension field via Key User Adaptation its BO query parameter is disabled and hence won't be able to be searched.
You need to add and make visible the extension field via Key User Adaptation for it to enable the BO query parameter and become searchable.
Extension Field; Search Results; Basic Search; Query; Values; , KBA , AP-RC-UIF-FLX , Page Layout & Key User Configuration , How To