I would check the mojoPortal system log for any clues under Administration > System Log
Most likely kind of problem would be slow connection resulting in request timeout or something like that, you could put a large executionTimeout on the httpRuntime element in Web.config if you determine that it is caused by request timeout.
I would also look in the mojoportal log for application start and end events, if those events are happening frequently it means a low memory hosting environment which could also cause such problems.
Other than that it would be network issues outside the control of mojoPortal.
In good hosting it should not happen and does not happen in any of my installations. It is definitely not a bug in mojoPortal.