To resolve this, Store Value should be checked and the field should be applied to the Transaction type.
1. Navigate to Setup > Customization > Transaction Body Fields.
2. Look for the field and click on its name.
3. Mark Store Value.
4. In Applies To tab, select Sale.
5. Click Save.
On a similar case, when the field is not applied to its corresponding transaction Type, inline editing will not be available for this field when viewing on lists or custom Saved Searches.
Note: Be sure to test first before applying this change to existing custom fields as the change impacts how the fields behave. Also note any message alert popup when saving custom fields that have been modified.