I have a third site that I was planning on pushing the AES-NI to, and I think I will try that over the weekend - I will have to wait and see if it crashes that.
The greater brother of yours SG-4860 will be able to push 500+ MBit/s over IPSec VPN tunnel and this stable
as a rock, so perhaps it will be more pending then on the lower power or a miss configuration perhaps.
If it doesn't, it's more than likely hardware related.
Do you really think that the hardware is malformed or buggy because your IPSec VPN is failing?
Hm, I am not really sure but you got two support calls for that actions like explained here in that case.
Did you ever thought about that, to take one of this to solve that issues by professional support?