It seems evony is changing, they have almost admitted its a bug.

Dear player,

Thank you for contacting Evony Customer Service.

Sometimes the star level up may fail at 100%, and it's automatically done, we can't interfere. Please understand our position.

If you need any further assistance on this issue, please feel free to respond in this ticket.

Best regards.

Customer Service

Evony Team

At least its not a couple denial