Since your cloud server is running Softether have you thought of just running the Softether software on your AR750, and use Softether to bridge your sites together without OpenVPN? Softether has its own VPN protocol which is multi-threaded and secure. Unfortunately there is a lot of bloat in the current GL iNet firmware, and with the AR750 only having 16M of flash, the Softether plug-ins do not fit. You would probably want to run the generic OpenWRT firmware for the AR750 which uses a lot less flash and would allow you to install the Softether plug-ins. As you are using the AR750 for a very specific task, there is no reason to run the GL iNet firmware. The Softether Windows based GUI would give you a nice interface to manage all your VPN routers remotely.
I have used Softether for years on my VPN servers. I have my own custom installation of the SoftEther client running on the GL iNet firmware on my travel AR750s, as it has a lot more flash than the AR750.