My AC87U has been working nicely for over 2 years, and was a noticable upgrade from the AC68U. Though now it's started failing, giving me issues similar to what others have been reporting in this and other threads.
It started around a month ago with 5 GHz WiFi devices suddenly disconnecting and reconnecting several times per minute for a while. After that, they work again for a several hours or a few days even until they start disconnecting/reconnecting again.
The 2,4 GHz WiFi and wired connections don't have this issue. But just yesterday the WAN connection started disconnecting randomly, requiring a reboot of the router to reconnect.
Power cycling, re-flashing, restoring to factory defaults and replacing the USB SSD drive attached doesn't help.
I guess it's time to upgrade once again, this time to an AX88U...