After updated multiple systems to CU 177, everyone of them needed a manually “Save and restart” via the Webfrontend in the proxy section.
The problem is caused by the removal of the SquidClamAV addon. CU177 won’t rewrite a new proxy configuration during the update and trys to use the now unavailable proxy helper and so it cannot start. After a manual save and restart (via the webfronted), the proxy is functional as expected because of the new written configuration.
Maybe it would be helpful for others which has not updated until now pointing to this fact in the blog entry for CU177?! 