With the release of Update 1.20 technical issues with the creation of battles in Strongholds occurred. We decided to temporarily disable Stronghold battles including Skirmishes and Advances. The other Stronghold features including Clan Reserves and Tour of Duty are not affected.
We are sorry for the inconveniences and apologize for the issues. We are working on a fix and will share information about the resumption of stronghold battles as soon as everything is stable again.