Just a small update. Two weeks ago I had an ISP outage and thought the problem was with the tuf-ax5400 and so the first thing I tried was a reboot of the router. Since then, the tuf-ax5400 has been working flawlessly with an ax-55 as a node connected via powerline. I even enabled ddns and traffic analyzer (which was giving me some trouble after a few days of usage in previous firmware versions), and everything is running smoothly. My next step is enabling an OVPN server (when I have time...). Free RAM is currently at 148MB.