169.xxx.xxx.xxx Ip Adresses

Im having issues with clients connected to out guest network. We recently changed our comcast wireless gateway for a comcast modem no wireless. We manage our wireless conections via 2 access points.But since like 2 weeks ago we are having issues with some devices not connecting to router/modem or not getting an ip address from device appering on device 169.xxx.xxx.xxx addres. This is a guest network for our customers, thisis a bug facility and average 80 devices/clients connecting everyday.We have 493 known devices/clients on the last week only. Comcast changed the gateway from wireless (since we dont use the wireless featuress anyway) to a modem/router only. They said the issue was that the previous gateway "wasnt pinging ipv4 addressess" thats afected old iphone and android phones? After changing we have no issues for like 5 days, and again many devices start having issues obtaining an ip adddress from modem/router showing wireless connection but with autoasigned ip address starting 169.xxx.xxx.xxx do anybody can have some insigth on this?Thanks

We have another exact modem/router with 4 access points, same brand same configuration, but with only 60 known devices / clients working perfect, thats why we think the ammount of users saved on router could be an issue??