UITK Template Containers don’t propagate events to children. For example, I have an UXML document Inventory. In Inventory, there are custom Visual Elements that listen for mouse events RegisterCallback<MouseUpEvent>(OnMouseUp.
If I put that Inventory UXML directly in UI GO, all events register correctly, when looking at Event debugger, those custom Visual Elements are the ones that receive events.
If I create a new UXML that merges multiple UXMLs into one UI, each UXML is put into a Template Container. However, now mouse click events don’t register correctly. Looking at Event Debugger, only Template Container receives events. Visual Elements that previously received events now don’t, tested both in code and in Event debugger.