The little magnet on the outside of your holster has fallen out. Simple as that. It has taken me two days and about 3 hours of research, tech support chat, scrolling through knowlege bases just to discover that a cummy little teeny magnet is the culprit.
Look below the clip and if there is a small round empty indentation then that is exactly what has happened. Used to be a little magnet there.
Now the question is: where to get a replacment magnet? It's a .02 item! But a new holster is $19.95.
I have had zero luck finding a source for magnets or some idea of what size and strength magnet is needed.