Slate Plus (GL-A1300) WG VPN connection freezes every 10 minutes

That’s my understanding.

If I were in your shoes, I’d pull the (Opal (GL-SFT1200)?) & set it as a WG Client to the Slate Plus acting as a WG Server as a 192.168.x.x/24 server… after resetting both devices back to stock on their most recent firmware, accordingly.

wg show & logread -e wg via SSH would be handy here. See below: