Auth Fail when connecting 2nd Asus Router as client

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Hi there,

I have an Asus Router as OpenVPN server. Seems to work fine. I have 3 other Asus routers to connect to server at other locations on different internet connections. I can connect one router as a client fine and all is working. I can connect a second connection via Windows fine at the same time.

But when I try to connect a second router with different user details I get auth fail. If I disconnect the first router and reconnect the second router the second router connects fine and works perfectly. I just can't connect them both at the same time.

I've tried for 2 days myself to try to fix and search the web but I'm out of ideas and things to try now. I'd really appreciate your help.
.