Based on the time you posted in Help it's likely a combination of:
Feeding between 08:00 and 08:15.
Site update lag between
www.flightrising.com and www1.flightrising.com.
In order to reduce server lag dragon energy does not drop all at once at 08:00, 16:00 and 0:00. Instead it gets staggered by age and takes up to about 15 minutes based on server load.
The lair page where dragons are fed is on
www1.flightrising.com but it displays information from
www.flightrising.com as well. This can cause conflicting data to be displayed until the sites sync up.
The way this error usually happens is:
1. Dragon energy bar drops in the lair but has not yet dropped for all dragons server-side on both sites.
2. Player feeds lair but only dragons that have had their energy drop recorded are fed.
3. Dragon energy server-side drops for another group of dragons.
4. Lair reloads once feeding is complete and the group of dragons whose energy had not yet dropped in #1 show as still being hungry.
Repeat 2-4 until both sites update energy drops, dragons are fed after all energy drops and both sites update with full energy.
This is not to say it can't also be an error--feeding during this time can get lost because between both sites updating and everything else going on it can happen but it's not as likely.
I generally just avoid feeding in the 15 minutes or so after the above times to avoid this happening. Try feeding outside of that time to see if it happens again. That would definitely be a bug and should be reported in a Contact Us.
