Christian,
If you would, please post details of your setup - what model iPad, OS it’s running, Zwift app version, information about your WiFi network etc. Dave has posted a guide to getting support, here:
https://forums.zwift.com/t/guide-to-getting-useful-support/425781
If you haven’t seen it already as well, we have a monthly megathread of resources. They’re not specific to troubleshooting but the first link in it is to a list of current app versions.