Hi -
I know this was an ongoing problem for us, running Unity 4.2(1) until we applied ES52 and 56. You didn't mention your specific Unity version, so I would always recommend checking with TAC before applying on your own server, or at least test. Any ES applied requires a short Unity outage and I break the mirror set before applying these too. If you are running 4.2(1), I think the ES are available for download online.
Ginger