As avast secureline basically only tells to connect through a certain server, I suspect the culprit is IOS.
I would say mention it on their webboard (if they have it) and see if others have the same problem and/or a (possible) solution/explanation.
It sometimes happen that things are not working properly after updating the OS.
Sometimes, removing the application completely and installing it from scratch is solving the problem.
As I don't have any iOS device to test/check things, this is about all I can tell you.