Hi Thomas,
Our developer finally find the reason of that.
That’s because the special session handle mode for web farm, it saved the session in the first server which receive the request, but hadn’t sync the session to other machine in web farm group. But our map is using session to save status and sync between client side and server side, so the other machine cannot access the session and can only render as pink tile.
The solution is set session state mode to SqlServer or StateServer.
Please view here for more detail solution: https://dotnetcodr.com/2013/07/01/web-farms-in-net-and-iis-part-5-session-state-management/
Regards,
Don