wired issue with placeHolder of the lightning-output-field in lwc

Question

I'm using lightning-output-field to output some of my record's field.

It is known that if a field's type is lookup, the component of the field input will have a placeHolder which says 'Searching objectName...'

But I meet a issue that some of the fileds will not show the name of the Object, instead it will show 'Searching undefined...' Other lookup fields will show properly, however. I can not tell what's the difference between these fields.

// this one shows properly
<lightning-input-field variant="standard" disabled field-name="RF_PROPERLY__c">
</lightning-input-field>

// this one shows undefined. The code is the same.
<lightning-input-field variant="standard" disabled field-name="RF_UNDIFINED__c">
</lightning-input-field>

Answer 1

Solution:

In the page layout of the object, drag the specific field to the info area, problem solved.