There are issues with some drivers for Windows 10 and Windows 11 when using IPsec VPN. The IPsec tunnel cannot be established. On both operating systems the issue is related to the driver of the network card. The problematic driver was deployed via Windows Update. In many cases the network card used was the Lenovo USB Ethernet adapter. Many customers reported, that the IPSec tunnel is working over wifi while it is not working over wired ethernet.
As example, in Windows 11 the FortiClient is preventing the IPSec connection and showing the following error message instead:
An update to the latest driver did not help. To be able to solve the issue, an older network card driver had to be used.
Not working Realtek driver= 1184.108.40.2063
Working Realtek driver= 1153.8.20.0608
Not working Realtek driver= 1153.13.420.2023
Working Realtek driver= 10.59.420.2023