If the traceability widget does not load, it is possible that you've introduced a cyclic relationship between configuration items. 

A cyclic relationship is one in which one or more configuration items are referencing each other in a way that would cause a loop in traceability. For example, if there are two requirements that reference each other as a 'parent' then this would be considered a cyclic relationship. This would create a cycle in the traceability due to one of the requirement items being considered both a child and a parent to the other requirement item (and vice versa). Additionally, a configuration item that references itself is also considered to be a cyclic relationship.

A cyclic relationship between items could cause issues in your traceability and create large loading times when trying to view your trace matrix. It is best to avoid these types of relationships due to the constraint that it can put onto the traceability calculations.

Examples of cyclic relationships could be seen in the image below. 

Figure 1: Cyclic relationships that should be avoided