This quite expensive and very elegant wifi router started dying very soon after the end of warranty.

Connections:

* WAN, 1 Gb/s service both directions (the real speedtest.net is about 160/90 Mb/s)

* WiFi all 4 enabled, connected 5 GHz new laptop, new audio receiver and 2,5 GHz guest network old laptop

* LAN 100 Mb/s Sony TV

* LAN 1 Gb/s Synology NAS

The router quite often diconnects from WAN (internet) and is generally very slow. If I download a file from the NAS to the laptop, the speed is about 33 MB/s (quite slow for a 5 GHz network with 866,7 Mb/s theoretical speed) and the internet is always diconnected during the transfer. Upload to NAS is about 25 MB/s and internet works fine during this.

The internet is sometimes disconnected even during no load at all. At all time, I am able to load the servicing webpage of the router, but loading it always takes a few minutes as opposed to expected few seconds when the router was new. The LEDs on the router used to shine normally, now they barely glow and only if you look at them in total dark. 

What is happening to this router?

Thank you for any hints.