Process Builder not triggering from a formula date field.

I’m trying to create a Process Builder process that sends an email alert 3 days before an invoice is due. It is based on a fomula field called Days Until Invoice Due which calculates the number of days until the Invoice Due Date date field. The process works fine when I manually change the Invoice Due Date to make the Days Until Invoice Due = "3". But, the process does not work when the Days Until Invoice Due is changed through the automation of the Formula field.

Here are the Conditions for the Action: