Settings - setup - Mobile Router Setup ... turn off wifi tethering is not marked

Hi all. "Settings - setup - Mobile Router Setup ... turn off wifi tethering is not marked" turned out to be my problem even though it's not the solution to the Original Poster's problem. I have no idea how that setting was ever changed. The only thing I remember doing was replacing the router's battery (after which the router stopped being detectable by nearby devices such as my phone). Thanks Ksa3344 who  suggested this. It saved me a lot of grief.