Sporadic exceptions when calling UserSessionService.getSession()

In the virgo logs I'm getting an ExecutionException when calling UserSessionService.getSession (see attached stacktrace - sensitive info is overwritten with 'xx')  

vSphere client SDK doesn't document exceptions for UserSessionService or how to work around them.  Can we get any pointers on how to root cause these failures?  It's a linked mode setup (2 VCs) with a standalone PSC. 



Best,

Mike