10003: Layer doesn't have an attribute index on fields used for a join
One of the join fields in your layer does not have an attribute index. Using join fields with an index results in better drawing and query performance.
Solutions
Do one of the following:
Review the draw metrics for this layer. If you are sharing the layer, review the data access metrics for the service. Learn more about performance in ArcGIS Pro.
If changes are needed, add an attribute index to the join field in your dataset. Learn more about joining and relating tables.
Additional information
Using joins that have not been indexed involves two technical aspects in the software: attribute indexes and attribute joins.
Attribute indexes can speed up attribute queries on feature classes and tables, and directly affects drawing performance. For most types of queries, it is faster to look up a record on an indexed field than it is to search through the entire table. Generally, you can improve overall performance using attribute indexes on key fields in your datasets.
Learn more about creating attribute indexes.
Attribute joins append the fields of one table to those of another through a field that is common in both tables. A join is used to attach more attributes to the attribute table of a layer. Using indexed fields for your join can improve performance in most situations.