What happened - The issue appeared to be a memory leak with the sync servers on our European deployment.
Why it happened - We do not deploy over the weekend which caused the server to not restart as it usually does. During this time period, the memory usage continued to rise on the machine until it ran out of available memory and thus created the incident.
What was done to fix it - We were able to identify the host having the issue and issued the reboot to fix the the host not being available.
How will this prevented in the future -
Begun an investigation of the memory usage of sync servers
Increased the memory and CPU on proxy servers
Added another proxy server for our European deployment
Updated our platform plans to include better alerting on this condition so that we can enable self-healing in future releases