Power BI data models will reject ambiguous relationships, in which there are multiple possible cross filtering paths
For example, a bridge table cannot have two many-to-one bidirectional relationships to tables (A and B), both of which have one-to-many, single-direction cross filtering relationships to table C
The model would not know (or try to guess) whether table A or B should be filtered prior to filtering table C
Inactive relationships, cross filter direction, and the CROSSFILTER() function provide additional modeling flexibility