I have the same problem mentioned in this thread. I have been able to access the title metadata using asset.value(forKey: "title") as? String, where asset is a PHasset retreived from a photo library. However, as far as I can tell there is no property key for the "caption" metadata.

I have the same problem. But I simply turn the mouse off (with the mouse power button on the bottom of the mouse), wait 2 seconds and then immediately turn it back on. Then click a few times and once the mouse reconnects it works fine until the mac goes to sleep again. Irritating, but not a show stopper.