Yeelight JIAOYUE YLXD04YL 450 does not connect

Good morning, I have a problem with Yeelight JIAOYUE YLXD04YL 450 lamps, since I changed modem I can’t register them on yeelight app anymore, I have tried several times but I can’t, the modem I am using is a TENDA 5G03 , yeelight app settings are China server, I am in Italy. Everything was working fine before.