I contacted Panasonic support and got a pretty fast reply. The only fix is to take the battery out of the glasses, power off the set, power it back up, put the battery back in and try again. After replacing the battery it worked as its supposed to, so not at all clear what went wrong the first time. There is a help screen for the battery removal, but basically you put a little screwdriver or knife blade in the small slot at the top of the batter compartment and pry and it pops off. Then note the battery orientation, take it out (take both out if you have 2 pairs), then put (both) back with the set powered off.
Just as an aside, another item on this set that confused me was the CATS setting. It should be renamed AUTO-BRIGHTNESS. The default is on, so in the evening the set would suddenly get dimmer (too dim) and it took me a while to find that setting to turn it off. If you could set the amount by which it auto-dimmed that would be fine, but as it is, its too much.