Answering my own question, since this seems to be impacting a lot of developers.
Voice commands changed a bit in XE16. Unlisted voice commands, like the one specified in your configuration, now require an additional permission. Add this to your manifest:
<uses-permission android:name="com.google.android.glass.permission.DEVELOPMENT" />
When you’re ready to release your Glassware, you must use a built-in static voice command. XML for this kind of command would look more like this:
<?xml version="1.0" encoding="utf-8"?>
<trigger command="START_A_RUN" />
Where START_A_RUN is one of the items from this list. If none of the listed commands are appropriate for your Glassware, you should request the addition of a voice command. This can take some time, so it’s best to do this as early as possible.