We couldn’t load apps - using costum domain

[Christian Schimmel]

If we use our generic domain abc.atlassian.net everything is fine, but when I use our own URL using reverse proxy wiki.abc.de we'll receive an arror:

"We couldn’t load apps - Refresh and try again."

This works for years but since some days it won't.

Our certificate for wiki.abc.de is valid, atlassian license is valid and we don't have any apps installed. What may be the issue here?