Two flights in a row now, with voice control, after I get "Flaps Full" done, I am calling for the Landing Checklist. The app recognized the command, but the FO never says anything in return. In the app window, it looks like the Landing Checklist is active, but it's not actually doing anything. I've never encountered that with button control before. Any idea what the reason might be?

In the Info Center, there's a LOG that will show you every thing the speech system has heard.

Please post a screen shot of that log.  If "Landing Checklist" was detected, it'll show up in the Log.

Also, try speaking "Cancel Checklist", then call for the "Landing Checklist".