I've just had this happen to me on a model I've been calibrating with.
I discovered that if I have "Allow single extrusion fill" selected and I adjust "First Layer Height" at 109% or above, the software freezes at calculating infill. If I go back to 108% or below, it works fine.
Also, selecting "Allow gap fill" works either way, like others have stated.
Not sure if that helps. Just my experience.