Have you tried "assisting" the fold when you activate it?
Had this once or twice on my Scenic.
Get someone to activate the switch and manually open the mirror with your hands gently at roughly the same speed as it would be if powered.
You may hear a loud click as the mechanism inside clicks back into place or frees itself up.
This is designed to disenguage if it's been bumped or forced but (as mine was) can just get stuck due to no lubrication and dirt inside.
When it first happened to me I thought it was fooked and it would be a dealer visit.
Now and again I squirt a blast of WD40 in between the mirror and the holder which helps a bit.