As of 2017-Jan there is an issue with 2.4Ghz band on the R6250 with the Advanced Tomato firmware. I also found this post https://www.myopenrouter.com/forum/what-hell-happened
I lost some static ip entries while using dd-wrt due to the known issue of how the page UI is very old and not really user friendly (great firmware though) – this drove me nuts so decided to try the Advanced Tomato on the R6250 – great UI. The Advanced Tomato UI worked great, firmware was great except for the 2.4Ghz band; the router page will show that the Wifi is good but none of the devices will be able to connect, tried various settings power etc, will show up then disappear and devices will not be able to connect. Searching the web brought up the page on myopenrouter listed above discussing the same issue. Switching back to stock/genie and maybe ddwrt.