I bought a DSL-N55U in 2015 on recommendation of someone on this forum. It was ok as a modem/router but excellent as a router. I converted the it into a pure router in 2015 and never looked back. Wifi has been rock solid over the past 5 years but security updates stopped in 2016 with a beta firmware where a few security holes were fixed.
Having had good service from the hardware of the N55U I decided to upgrade to faster wifi as I had purchased a laptop with ac wifi and the N55U is only N. After trying the ZyXel VMG3925-B10A (second hand) and VMG-8924-B10A both had weak wifi performance. So I decided to buy new as I had no come back on Second hand out of manufacture routers.
So I intially went for RT-AC58U but after a week found the wifi unreliable and TV streaming was dropping out. So I did some research and located a review that recommended the RT-AC1200G+ so sent the AC58 back for refund and bought the 1200G+ in Feb.
Every now and then when downloading a 1gb file on the 1200G+ on a wired connection it would get to 886mb then the PPP session would drop. This was usually after the router had been idle overnight. I could then download the same 1gb file after the PPP session had re-connected several time and it was fine.
This became annoying when I was trying to update my laptop to Windows 10 2004 over wifi as it would download updates but the PPP session would fall over and the setup would fail so I decided after advice from Asus Technical support to return the 1200G+ for replacement. Which I did.
The replacement turned up on Saturday gone, (kudos Amazon) and has been on test since then. I did a basic Quick setup not using any of the advanced features like IPV6 or QoS. So far so good. After lots of testing the PPP session has stayed up through lots of large downloads and large file transfers over wifi which would also make the last one fall over too. I will test for a week before I start changing configuration gradually but I have noticed that when downloading on the faulty 1200G+, CPU use on the router was 100% but with this basic config and the new router the CPU use is 20% when downloading the same 1gb file.
The testing continues, so far so good.