Must be a misconfiguration of mod_remoteip.@Peter Debik There is no way that this should be enabled by default on new installs. This breaks all Apache modsecurity attack triggers and any Apache log statistics programs as the client address only reports 127.0.0.1 as the client address after enabling it.
At the end of /etc/apache2/plesk.conf.d/server.conf, there needs to be 127.0.0.1 added to the line RemoteIPInternalProxy.
@Peter Debik is that enough to forward to dev or should I open a bug?