Mail Won't Respond To Mouse Clicks

Since I updated El Capitan to 10.11.1 and continuing after a recent update to 10.11.2, Mail often does not respond to mouse clicks (to select messages, delete messages, etc.) I can't even click on the Mail window to make it active.

I need to quit Mail, re-open and then things seem to work okay. Until they don't. And I quit Mail, restart.....

And it's not just on one of my Macs, but both. At home and at work.

Messages seem to be very sensitive to the new swipe left to trash-swipe right to mark as unread. I use a Magic Mouse.

The swiping may be the culprit. Can this be turned off?

Have you experienced this? Any suggestions?