On iOS 13.6, the current version of the Jitsi App resets the custom meeting server URL at every app start. See the image below for our Jitsi server, correctly set, and a meeting can then also be opened. The second screenshot shows the settings screen, with the meeting server URL reset to the standard meet.jit.si. Expected behaviour would be to leave the custom URL intact. I am not sure as of which App version this faulty behaviour occurred, unfortunately.