Intermittent issues are always a challenge to troubleshoot. You mention that the Answer Indicator says "Yes-PostRedirection." That could mean that the call was "answered" by the voicemail system after being redirected but I'm not familiar enough with the call logs to be able to answer that. Since it appears you have a hunt group, I wonder if the hunt group routing could also cause the PostRedirection entry. Have you compared these logs to a call that was successfully answered to check for that entry?
Intermittent issues could also be caused by some brief network or internet registration/connectivity issues or the system not thinking any agents are available to take calls. If you haven't already, you may want to open a TAC case the next time it happens so they can review your configuration, the logs and your environment.
@smonaghan, we will need more information to help with this. Since we don't have much information, here are a few things to check. First you'll want to verify the settings for the number(s) are routing correctly and that they're not configured to send directly to voice mail. Also verify the device is registered to receive calls. If this is a pilot/hunt group number, verify the front desk numbers are included in the routing. If checking these sttings don't resolve the problem, please provide additional details regarding the programming and routing.
Good luck.
