Firewall behind ISP Router

Hello,

You may review the logs using below:

support.sophos.com/.../KBA-000006520

Hello,
what problem are you seeing? What does the connection look like in the GUI? What is in the log viewer under "VPN"
Are IKE packets arriving at the firewall (packet capture with filter "port 500")
How long has the problem been occurring?
Sophos recently made a change to IKE which can cause IPSec problems with third-party devices. (In our case, the Cisco ASA allowed IKE through, but not ESP data)
may be, IPSec is used on the ISP-router too ...?