For extensions from the CDB that have already been installed and for which the version check is still set up without SSL, the version check cannot be carried out. Since phpBB displays the version of a failed version check in the same way as it does for an extension without a version check, the administrators are not informed about the failed version check and therefore do not know that they may have an outdated version of an extension.

Reference: https://tracker.phpbb.com/browse/WEBSITE-1434

PR with a possible fix follows.