We have identified a problem with our DHCP configuration for Cloud Servers in the network 188.8.131.52/24. From 2018-04-25 at around 23:00 CEST to 2018-04-26 at 10:45 CEST our DHCP servers were pushing an MTU of 1550 Bytes to all Cloud Servers in that network upon renewal of their DHCP lease. The problem has been fixed and the correct MTU of 1500 Bytes will be pushed to all Cloud Servers upon next DHCP request.
However, because the lease time is 24 hours, it could take up to 12 hours (half the lease time) for servers to send the next DHCP request and receive the correct MTU value. In order to mitigate the problem beforehand, you can either reboot your server, toggle your network interface or manually issue 'ip link set mtu 1500 dev <public_network_interface>'.
Please accept our apologies for the inconvenience this incident has caused for you and your customers. We keep doing our best to prevent such a situation from happening in the future.
Please do not hesitate to contact us if you have any follow-up questions.