There is currently a bug on Clan Pages where the banner does not display on the Clan Info tab. Clan Pages are very buggy and outdated as they are, but hopefully, this will be looked in to and fixed soon.
It appears as it should on other tabs for me: ~ Sicariu
Wont update on RuneClan either which is something a lot of clan leaders and members even use to track their Xp gain and their Clan, friends.. etc. Please fix this. It's something minor but its not a fault on RuneClan's side as they receive all their data from here.