(BTW, the model field doesn't let me select the actual model which is anb AC5400 tri band gaming router. )

The router has beeb proble free since I bougt it 2020. 2 days ago after returning from holiday I noticed an amber light plus wifi performance waw poor and no 5 ghz option (SSID)_. I logged inot the router, couldn't see any problems. upgraded the firmware to the latest (and the reapplied it a second time, just in case). 

Rebooted numerous times, plus the Virgin router (set up as modem)., still have an amber light and only 2 ghz. 

Two interesting points. 

When i logged into the router the SSIDs all had the same name (for 2.4 and 5 options), so I renamded them back to what they used to be. Found this odd, they've always been different for obvious reasons. 

Also, as advised in another thread, I set 5 ghz -2 to channel width 80 and channel 128 (although it displays 36 when i look at the status). 

None of this made any difference. 

Second interesting point - my second router (different model) which is an e3xtender for the back of the house and ocnnected via CAT65 to the AC5400) works fine for 2.4 and 5 Ghz. Wifi performance is fine. 

So to conclude, its a wifi only problem with the AC5400, cabled items are working fine, plus the extender.