Setting up a new router that has 2.4 and 5g. The default settings has 2.4 on auto channel selection and 5g on channel 153(not sure why). Do you usually set a certain channel or use auto?
I don't have much nearby 2.4Ghz radiation. I pick my channel (1, 6, 11) for 2.4Ghz and 153 for 5Ghz. If you have problems with 5Ghz, try channel 40. Some adapters have problems with the upper channels. 40 is a universal 5Ghz channel. If you have an android phone get a copy of WIFI Analyzer -- https://play.google.com/store/apps/details?id=com.farproc.wifi.analyzer&hl=en It can show you any competing WIFI networks.