Modem/router - Known devices reconnect but can't get access to the net?

[gizmo1990]

I have an ASUS DSL-AC88U AC3100 modem router, which I've been happy with. However, I've been experiencing an on/off issue (probably since I first got it) when known devices reconnect to the network. For some reason when they reconnect they can't go online? However resetting the modem fixes it and everything is fine, they connect to the net perfectly.

Does anyone know what could be causing this? It feels almost like some kind of setting. Like a timed device limit or something? But I can't find any info on it.

Any advice much appreciated.

 

[gizmo1990]

Finally back on this as I'd mislaid my password and couldn't login. Found it now though!

Thanks for all the replies so far.

This is a total guess. Could it be Firewall settings and the way ports are assigned? Can you look at how the firewall works for this router?

All the firewall settings I can see are 'turn firewall on/off' That's it! There's a URL Filter section and a Network Services Filter but none of them have anything entered. Everything I've read about enabling firewall say that you should leave it on. Is that correct?

Is the firmware on the latest version (looks like 2021 was last update just for a CVE). Failing that, have you tried a factory reset?

I've just updated the firmware now.

Any other thoughts regarding this would be most welcome!