I thought it was just me. I’ve been experiencing occasional freeze-ups for a while now. Everything locks up. The clock stops, and the mouse cursor won’t move. I need to do a cold restart.
This is the first mention I’ve seen that other people have had a problem. I’ve suspected a hardware glitch – which is annoying, because my MacBook Air is about a year old. I’ve been putting off calling AppleCare.
I hadn’t seen freeze-ups on days I reboot, so I rebooted daily.
As I write this, I’ve just updated to 10.11.5. The release notes don’t give any clear indication of fixing the problem I’m having, but you never know.