Can't use chat with WebRTC in browser

When I connect to a conference using a WebRTC capable browser, it works fine. But when I open the chat, the chat window appears, but I can’t type anything in it! What am I doing wrong?

Is this on meet.jit.si or your own server?

Not meet.jit.si, a free server of a linux group.

Thanks for the hint. Seemed to be a server issue. Other servers work fine.