Unable to add name to past event invite list

I have troop admin access and was putting in attendance for a troop meeting last week and noticed a name missing. I was able to go into edit event and add the person, but then the event would not save. When I went back to the event, it dropped the added name as if I never changed anything. tried several times with no luck. Event code: scouting.org/events/editEvent/5782108

hmm - this works fine for with before and after attendance is started.