All settings have been checked in the Telecom Shop. (Very good service) I spoke on the phone with Google Help for at least 15 minutes and am still in contact via email. Nobody at Swisscom has heard of this problem either.
When I leave the country and enter A, DE, FR, ES, a download is only possible via WiFi. If someone could be found to try a stay abroad, at least I wouldn’t feel so “lonely”. Thank you very much