60F IPSEC VPN Stops passing traffic

I deployed 2 different customers with a 60F at their main office and 60E's at their 3 remote sites last weeks. The VPNs come up and stay up, but at random times the VPNs will just stop passing traffic. If I bring the tunnels down from the main office, things immediately come back up (due to auto-negotiate and auto-rekey being enabled) and traffic usually starts flowing right away again, but sometimes I have to bounce the tunnel on the remote device as well. These are very basic setups, which I've done many times before with 60D and 60E devices. Anyone else have issues like this with the 60F? Everything is running 6.0.9, and I'm afraid to try 6.2.3 since the known issues list is pretty long and I think it will do more harm than good to upgrade. I'm working on getting them swapped for E's to see if it is the new hardware series.