Availability Group is a Klingon Warrior
One thing you should know about AG is that it carries the sign of house it was born in, like a Klingon Warrior.
One of the cool features is the Availability Group, which picks up where Database Mirroring has left off, is that you don't have to configure as many things in SQL as far as which server does what goes. Mostly, it has offloaded lots of inter-server communication bits to Windows Server Failover Clustering, which is great for several reasons. One of them is separations of concerns - Windows Admins can go about setting up the failover cluster, manage the SAN and what not the way they like - so SQL people can go in and take care of the SQL-ly business.
Now, as a natural result of AlwaysOn Availability Group needing WSFC cluster, this happens.
If you delete and re-create a WSFC cluster, you must disable and re-enable the AlwaysOn Availability Groups feature on each instance of SQL Server.
Sometimes those little boxes with yellow exclamation marks are actually worth reading!
Simply put, every AG bears the signs of WSFC cluster is was born in, and they have to match in order to work. So, if the house it was born in was defeated in a glorious battle and no more, it needs a new house and it needs to carry the sign of the new house. Something to keep in mind. That's all for today!