To avoid login errors or messages and also to avoid certain problems with server-to-server connections we installed proper certificates for the secondary domains today.
We had to restart the Jabber services several times, sorry. The ejabberd config file isn’t commented very good, also Google didn’t tell us the correct settings in the first place. But everything works fine now.
PS: For old SSL connections to port 5223 there are no dynamic certificates. This just isn’t possible because of how SSL works.