To get a better idea of what is happening Id recommend...
1. Disable Windows Defender and test the VPN again. If it works, you know Defender is responsible.
2. Try this with the Cisco IPSec Client. If it fails, turn on the VPNClient logs (Logging>Enable, Log>Log Settings>3-HIGH, Log>Log Window)
3. You can also enable "debug cry isa" and "debug cry ipsec" on the router to see if any crypto packets are received
4. You can download a sniffer tool like Wireshark on the client and see if any vpn packets (udp 500, udp4500, tcp10000, esp50, etc) leave the physical or vpn adapter interface of the computer.
-heather
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