are you using DHCP ? This is a know issues with old DHCP configuration due to the unicast flags on DHCP discover messages from Apple devices and the same has been fixed on JDHCP design. Request you to use JDHCP config and check.
If you already have JDHCP config , please do a pcap from apple and compare it with working device to see if there is anything difference.
Run below command to see if you have DHCP or JDHCP
root> show system processes extensive | match dhcp
29644 root 1 76 0 85792K 11700K select 0:00 0.00% jdhcpd ----> Here its JDHCP
root>
Sampel JDHCP config:
set system services dhcp-local-server group JDHCP interface ge-0/0/0.0
set access address-assignment pool JDHCPVR-POOL family inet network 6.6.6.0/24
set access address-assignment pool JDHCPVR-POOL family inet range JDHCPVR-RANGE low 6.6.6.66
set access address-assignment pool JDHCPVR-POOL family inet range JDHCPVR-RANGE high 6.6.6.67
set access address-assignment pool JDHCPVR-POOL family inet dhcp-attributes router 6.6.6.1
ref: https://kb.juniper.net/InfoCenter/index?page=content&id=KB26898&actp=search