Make sure, a. App version is 3.4.1 if you are holding an IOS; and for Andriod one, it should be 3.3.6; b. Is your Hub version a V17? If not, upgrade its version to V17. c. If the above failed, be sure IP addresses of all lights are under the same subnet (not the same WIFI)---these could be virified at the settings of your main Router. d. Last but not least, just re-add lights of Hue one by one at our app ( donot delete the old one) and make a test then