I decide to write this tp prevent situation i face few days ago. Problem is when u after upgrading close your browser. Sometimes upgrading is enrolled back to previous lvl. It seams that data about upgrading is forwarded to game server with a some delay time.
If u successful upgrading any unit don’t leave game. Instead that move to other location in map and move back after that. Is good also make any battle (pvp or pve) to have some more confidence :)