I would recommend you go back to the GL firmware, latest testing version, openwrt-ar750s-3.101-0212.img, from here:

https://dl.gl-inet.com/firmware/ar750s/testing/

The img file is used in uBoot, the tar file is used in the GL UI upgrade page.

You can access Luci from the GL UI menu, More Settings → Advanced.

I still recommend you switch to wireguard for all your devices, but do what you did again using the GL firmware.