R6220 slow wireless connection

I have Xfinity thorugh Comcast as my ISP, and I have been experiencing slow speeds through both my wired and wireless connections. Several months ago I saw a post about this issue, and I followed the advice to reset my router to original factory settings. This resolve my issues, but not they are back, especially after the recent firmware update.

My question is, must I go back to factory settings every few months to keep my connection speeds up? My custom security settings make this very inconvenient, because I have to reauthorize every machine that connects to my router. Is going back to factory settings the only way?