Re your OP, I think you'll find AA aren't doing PPP resets. That it's the router doing it.
Are you using it in combo mode, or with front-end modem such as an HG612? If using an HG612 then rebooting the ZyXel of course won't bother DLM. It was when I was trying it in combo mode and IPv6 at the same time I ran into trouble.
As a point of interest, but relevant once you get it stable, are you doing an IPv6 BQM? Don't forget, if you are or might, that the IPv6 address thinkbroadband detects is your device. Not the modem/router. You have to substitute the correct one.
They really should have stopped supplying this ZyXel as soon as they used up their stock of them ages ago. By now if they had any left they should have written them off, or at least informed the buyer they should be used for IPv4 only. Before the user signs up for broadband with them
. Basically, it is no longer fit for purpose in the form advertised.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. 200GB. Sync 73724/12601Kbps @ 600m. BQMs - IPv4