When I try to update my Debian 9 packages, I get:
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://download.owncloud.org/download/repositories/stable/Debian_9.0 Release: Die folgenden Signaturen waren ungültig: BADSIG 47AE7F72479BC94B ownCloud build service obsrun@localhost
I have tried removing and readding the GPG key as described here: https://download.owncloud.org/download/repositories/production/owncloud/ - to no avail.