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.

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