When searching in JQL basic it doesn't allow to search a field that has context applied to a sub-set of issue types if the option "Type" is set to All.

when selecting "All" issue types, it seems to imply, "If any of the other filters apply, filter based on those." I might not be aware or particularly concerned about the specific issue type, but rather just seek any relevant information for this project (or in Jira) regarding this customer.

For this reason, having to filter issue types first (and recalling which issue types are associated with a field) before filtering for the field's values might not be the most intuitive approach. Although it could be considered "expected" behavior, enhancing the intuitiveness could lead to an improved user experience.