I have an issue with one site connecting to head office. There are three other sites already having site to site VPNs with head office and they work reliably. There is not much to get wrong in the wizard, it is simple enough but with this site the VPN gets set up but the remote site is receiving no packets from the head office. Looking at the head office ASA I see it is receiving packets but sending nothing.
However, sometimes by rebooting one or the other firewalls (or even both) the VPN will work correctly for anything from a few hours to a few weeks before reverting back to the situation above.
All the branch offices are running OS version 9.6(1)
Does anyone have any ideas please?