If you hold the pause button and a group becomes "inactive", it will remove itself from the list, leaving a blank space in the list. These groups become inactive when the leader goes offline, or the group becomes "stale".
Groups often become "stale" earlier than they should when you have misconfigured time settings. The score keeper usually "nudges" your time and corrects it so that you never know anything was wrong, but after todays patch the scorekeeprs aren't able to log in.
Check your time setting in windows. Check your am / pm, time zone, daylight savings time, etc.