There is a known limitation about join() functions that are not supported when running in live queries — the details are explained at Join Operation and Optimization.

This limitation causes these queries not truly running live in your widget, but running repeatedly instead, to show results that are as recent as possible.

When you create a widget with such a query, an indicator in the User Interface notifies you on how old the query is — that is, when it was the last time it has been executed (Just now, 1 minute ago, etc.):

Figure 196. Repeated Query Indicator