I think we adapted someone else's similar flow online. Doesn't 'apply to each' mean perform an action for each list item, anytime that item status changes?
When an item or file is modified, get the changes, and if the status reads as complete, send an email.
Edit: Actually, what seems to be happening is something others have mentioned: values change for no reason at random times. For instance, I saw another poster here say the values in their flow kept reverting to blank after signing out, or walking away, and coming back later. It just happened to me but instead of clearing the value field, it replaced it with another type of dynamic content that I never would have chosen on my own. VERY STRANGE.