I recently purchased an Asus RP-AC55 wireless repeater because my router was reaching only some of the places I needed it to, but it has caused more problems than solved.
Its inability to accept connections from any Ubuntu device is the primary problem. It won't work with any of the two laptops (two Zenbooks) and one old desktop that I've tried on two different Ubuntu versions (16.04 and 18.04), none of which had previously given me any WiFi-related problems.
Windows is installed on one of the Zenbooks, and when using Windows, the router connection is flawless. In addition, I've tested a few Android phones, and they've all had no trouble connecting to the repeater and the internet via it.
The repeater will crash, shut down, and reboot when someone tries to connect to it from an Ubuntu-based device. This is the second part of the problem. The repeater will reboot after a brief period during which the internet is unavailable, and a question mark appears on the wireless indicator (which is, incidentally, running GNOME Shell).
After some more testing, the problem is partially caused by DNS. My laptop connects to the router and doesn't crash if I manually set the IP address, and the terminal's ping test of 126.96.36.199 returns a positive result. However, nslookup and standard internet browsing don't work.
In addition to the crash, pinging anything before the impact is unsuccessful if I leave the IP address set to "Automatic (DHCP)". In addition to setting a manual IP, I attempted to manually set the DNS to connect the repeater to Google's DNS (188.8.131.52, 184.108.40.206).
Still, when I do that, the link crashes as if I hadn't manually set the IP and nothing pings. I also attempted to configure the repeater to use Google's DNS, but I could have yielded more fruitful outcomes.
Thus, I believe the problem is with both DNS and getting an IP address, the former of which I have no idea how to "fix".
As long as I can obtain the logs—some may be difficult to get due to the almost immediate reboot—I'm willing to provide any records you might need, but I haven't included any in this post because I'm not sure which ones might be useful.