We had problems with the vSphere client (not the webclient) :
-Inventory filled up the disk volume because it was writing logs (xhive) on the drive -> result server crash
-Web client shows outdated data even if you create new items in the web client they will not show up
-Loading.... showing in the vSphere client, especially after a reboot of vCenter.. not showing VMs, Datastores and Network on certain hosts.
-Reinstall of vCenter, didnt work.
-Change of SQL server didnt work.
-Strange behaviour with VDP 5.5.5.190, Not able to backup because of license errors and core service shuts down
Turned out to be vFRC, after disabling all disks on all hosts the problem went away, Should be resolved in 5.5 u2
VMware KB: After enabling Virtual Flash, VMware vCenter Server 5.5 consumes most of the CPU, memory, or disk I/O