2.4 band connectivity

Both my iPad and iPhone are having problems either accessing or getting negligible signal when connecting to the internet on the 2.4 GHz band (thro' Netgear dual band router) - this is new and before they worked perfectly. No issues with the 5.0 GHz. My iMac, Mac laptop and my wife's iPad and iPhone all work perfectly in the same location, same router etc. on the 2,4 GHz band. So its not an issue with the router or the internet service. I've done the usual reboots on both the router and the Ipad/Iphone to no avail. I can't work out what the problem is - why only my iPad and iPhone but not the other devices. Any suggestions??