I used to have the same problem on my Mango and Brume routers. However, for some reason things went back to normal. I also had to do the steps in your second post, but now whenever I restart the routers or disconnect/connect OpenVPN with policies, things just connect. You should note however that sometimes after a restart it can take a few minutes (about 3 to 5) to connect properly.
P.S. On the Mango I’m on firmware 3.102 and on the Brume on 3.104.
It seem the is a problem between VPN policy and openvpn. If i turnoff vpn policy then restart the device, most of the time the openvpn is working perfectly and it can be connect-disconnect-reconnect the vpn flawlessly.
i can only hope that next firmware update will fix the problem.