Your WIFI router may receive many interferences from your neighborhood, and these interferences change day by day.
To have the best performance, from time to time your WIFI router need to be re-configured.

part of Cisco Linksys
part of DD-WRT
part of OpenWRT
part of ASUS
part of Tenda
part of D-Link
part of TP-Link
part of Huawei
And others ...