Over shabbos my consecutive days counter got restarted. How did that happen? I was on the site right before shabbos and back on right afterwards.
StackExchange works on UTC. Right now in, say, NYC Shabbat ends around 6:30 so it's possible if not likely that someone would miss logging in by 7PM EST which is midnight UTC.
If that doesn't apply to you, perhaps you didn't do anything particularly active during the 24 hour day? I don't think there are clear guidelines about what must be done to be considered active that day. Possibly loading a page wouldn't be sufficient.
If you can document activity on the UTC-day in question (eg. a timestamp on a comment) then please post that information in a bug report on Meta.