Importing symbology returns a warning message in ArcGIS Pro

Description

In ArcGIS Pro, the symbology of a feature layer or layer file can be imported to another feature layer using the Apply Symbology From Layer tool. Sometimes, importing the symbology of a layer to another feature layer may return the following warning message in the Symbology pane:

Warning:   
Primary symbology relies on one or more fields that are invalid.

Importing the symbology after joining a table to the feature layer also occasionally returns the same warning.

Cause

• The Symbology Fields parameter in the Apply Symbology From Layer tool is not specified.
• The feature layer contains joins or relates.

Solution or Workaround

Note:
These solutions have been demonstrated to work with ArcGIS Pro when using a standard file-based geodatabase, but have not been validated for all RDBMS(s).

Depending on the cause, select one of the methods below to resolve the issue.

Specify the Symbology Fields parameters

When importing the symbology, set the Type, Source Field, and Target Field parameters in the Apply Symbology From Layer pane to match the fields from each layer, to define the symbology.

Remove all joins or relates on the feature layers

Remove all joins or relates on the feature layers before importing the symbology.

1. Remove all joins or relates on the feature layers. Refer to ArcGIS Pro: Remove a join or ArcGIS Pro: Remove a relate for steps and more information.
2. If necessary, re-symbolize the desired feature layer or layers.
3. Import the symbology using the Apply Symbology From Layer tool.
4. Re-add the join or relate to the desired feature layer.