The deadline was 10 AM, until a couple of months ago when I switched it back to midnight. So I think you're on to something there. It looks like the data points were being grouped with the 10 AM to 10 AM window starting the prior day.
When I reinstalled the Beeminder iOS app, the grouping changed to midnight to midnight. It looks like the iOS app is perhaps caching and not correctly refreshing the deadline for goals?
I'll be on the lookout for the new version of the app and let you know if that fixes my problem.