So I have a PC connected to my router thru a Cisco Wireless ac USB Adapter, the thing I found funny is when I am connected to the router thru 2.4GHz network, my signal strength is ~-68db which is great according to this link. But when I switch to 5GHz network the signal strength drops to ~-80db which is unusable at all.
Regarding the router location its only about 5 metres away, although separated by a wall.