Tapping the Configuration Item reference button in a record in mobile mode does not always return records.
This behavior is caused due to an out-of-box dependency between the Configuration Item column and the Company column. If a record has an associated company, only configuration items for that company are returned. If a record has no company associated with it, all configuration items are returned.
Associate configuration items with the companies associated with the affected records.
Note: A configuration item can be associated with only one company at a time.
This is also the way desktop mode behaves when the Company field is present on the form. If the Company field is not present on the form in desktop mode, the dependency is disregarded and the full list of configuration items is returned. But in mobile mode, the dependency is not disregarded even when the Company field is not present on the mobile view form.
Problem PRB1281929 "If Company is not associated with any configuration items, the Configuration Item reference icon returns no results in mobile mode although it does in desktop mode if Company is not present on the form" was opened to report this, but this problem was closed as Won't Fix.