My query gets stuck - but only in the one way I want to use it!

I have a query that returns a single document based on the value in a field of that document matching the value of a field of another document. This query runs when a button is pressed as part of a 18 action chain.

Problem is for some reason the action chain gets stuck at that query. I have put "sentinel" notification actions immediately before and after the query action, and the one before runs, but the one after doesn't so I know it's at that query action that it's getting stuck. However the query will run fine if I remove the match filter. But the query will run fine with the filter when I add it as a stand alone action on another button on the same page.

Does anyone know of any restrictions on running queries, perhaps as a chain of actions? At one point I think it worked, but the firebase prompted that it needed to create new index and after that- nada.

Any ideas people?

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