Path expression can be replaced with "&1.&2"

What causes this issue?

Usage of the path expression <association name>.<attribute name> can be
replaced with <data source name>.<attribute name>

System Response

Usage of the association in the path expression leads to an unnecessary
LEFT OUTER JOIN on the DB level

How to fix this error?

Use the attribute directly or the path <data source name>.<attribute
name>

Error message extract from SAP system. Copyright SAP SE.