it seems that my problem has been solved, I have now run against my own Openvpn server from pivpn for a few weeks without problems with UDP, the speed is good, probably only limited by the server...

@SomeNetEngineer good, then you have what you need for your initial question, now you can activate policy route and route all traffic out on the remote WAN.. there will be policy route to both...

@SomeNetEngineer what is your ip address pool? on this pool I never use same ip as my other interface, for the most i use a random ip10.12.33.0/24 for example or somthing in 10,x,x,x range

@SomeNetEngineer if you want to route all or some devices out to the remote wan, you create a policy route, choose l2tp in this example I route everything from the default lan out to the remote...

@SomeNetEngineer it is also not certain that you can reach the admin interface if you have not enabled admin from remote lan, I mean to remember that there was a choice for that in stand alone,

@SomeNetEngineer it looks correct but i am using controller so slightly different configuration. I did a test on the same thing here now between an ER841 and an ER605v2 and it worked right away....