iOS: Die Netzwerkverbindung wurde unterbrochen

Hello, I’m using Cryptomator for some time on my windows desktop and it works as intended.
Today I bought and installed Cryptomator on my iPad. After adding an existing vault on OneDrive I could not access this vault. I receive the error message “Die Netzwerkverbindung wurde unterbrochen”. I changed my iPad’s WiFi connection from job WiFi to a mobile hotspot via smartphone. With the cellular phone connection Cryptomator works fine, with the job WiFi connection it doesn’t. Any suggestions?
Thanks in advance - Sven