BUG? "Try Actions" not working

Thanks for a superb program!

Using KM 7.3.1 on OS X 10.11.6 (El Capitan) on a MacBook Air.

In the KM Editor the “Try Actions” button has stopped working (as well as the context menu, when present). This worked a few weeks ago.
This is true no matter what the action is.
But taking the same action and putting it in a macro, with a trigger, works perfectly.
Any ideas? (Tried, of course, a fresh boot, etc.)

This would indicate a problem communicating with the engine. I would suggest restarting - I suspect sometimes the inter-process communication system gets a bit confused.

Curiously, it took two reboots to straighten things up.