This occurs in multi day events when start time and end time are the same.
Eg. on the site I admin two events where dates were showing but not time of day. I noticed they both started and ended at 16:00. I set one of them to end at 16:01, and now time of day displays correctly for that event.
Eg. on the site I admin two events where dates were showing but not time of day. I noticed they both started and ended at 16:00. I set one of them to end at 16:01, and now time of day displays correctly for that event.