We had the same issue for weeks and finally resolved it with help from VMware. We use a VMware Data Recovery appliance (v2.0.0) and have the corresponding plugin for the vSphere client installed.
It turns out this plugin was creating an awful lot of connections to the vCenter Server when it was restarted, causing the memory to go 100%. After uninstalling the plugin, upgrading the VDR appliance to the latest version (2.0.2), and re installing the plugin from its latest release, the problem went away. VMware also made us upgrade the vCenter SQL Express database to a full edition, but I'm not sure that made a difference.
So if you have the memory leak issue and are using VDR, you might want to do the same. Good luck !