Hello @Don_Ferrario & @ReeXNeeX,
We have a similar situation and a ticket open with Peplink at the moment too (ticket # 9050173).
Based on this thread, the ticket may be related.
Our issue is Windows 10 Pro PCs (from our client & us with the all the latest windows updates) are not able to connect via IPSec to the routers.
Peplink’s engineers and support can connect just fine.
We have checked firewall, ISP, software, IPs (and other stuff too like the Peplink guide in this forum of “Setting up L2TP With IPsec”).
At the moment we have not been able to find a solution, rolling back to Firmware Ware 6 is not an option due to other required feature in the newer releases.
Hopefully, we can all work out together what is the cause and solution, over to you again @TK_Liew.
Happy to Help,
Marcus 