2 weeks ago
This method also worked for my 2017 model (Samsung UN58MU6100). All of a sudden, our TV couldn't see the wi-fi networks in our home. I looked, and sure enough, there was a firmware update that posted on January 9, 2019. Downloaded, unzipped the file, and dragged it onto a 2GB flash USB drive. Plugged it into the back of the TV. Only difference is that the menus have changed slightly from the instructions given above. Now you need to go to Support > Software Update and choose Yes when it asks to search the USB device. TV updated itself within a minute and now we're up and running with a solid wi-fi connection again.
Thanks to the user who posted this solution. You saved me the headache of calling support.