This problem is limited to iPads only and all other resources are getting a DHCP address?
I had a similiar problem but in conjunction with Cisco APs. The workaround was, to give the iPads a fixed IP address. That worked in our scenario, as the iPads were used as door tablets for meeting rooms. If your iPads are roaming (from subnet to subnet), this workaround would not be fitting your needs.
You may wish to check for driver updates or browse release notes for the products in use.