Here is the Items property for the Gallery:
Sort(
Filter('IBC Checklists', Completed = Text(CompFilter)),
Created,
SortOrder
)
I have a button on the page for debugging and it changes CompFilter to "true" or "false". I know that works because I also have a label that shows the current context.
I've also included a screenshot that shows that PA understands the context changing. It's "true" in the current image.

But the gallery doesn't change when I click the button and flip CompFilter back and forth. I was originally comparing Completed = CompFilter directly rather than converting to Text first and that didn't work either.
I'm very stumped.