Hi
Either a problem with your power supply not able to supply enough standby current for the over clocked memory, or it isn't stable enough to survive the transitions to lower refresh rates it sees in standby.
It is the cost of pushing things beyond their typical ratings.
To be honest given the extra latency you need to employ to drive the memory at 2133MHz it probably isn't giving you much real-world performance difference than running at 1600MHz but with lower latency.
Regards
Phil
