My Archer A6 is generating 2.4GHz signals with max link speed of 217mbps and showing as N217 in wifi scanners instead of N450 even if the device is just beside the router. Making the internet connnection slower.

This happens when the router is kept connected for few hours. The issue is resolved once the router is hard rebooted (keeping turned off for atleast 10 seconds) only to reappear again after few hours. Soft reboot does not resolve the issue.