N3048P Slow IP Addresses

We have been running in to a problem over the last year where random computers each morning are taking approx 15 minutes to obtain an IP address. It is completely random and is happening on different pcs each day on different switches. All switches are Dell managed switches. We don't have a very complicated network layout. Our current external support provider is pushing us down the route of changing all switch to HP Aruba as their recommended solution (they are a hp house) When I run a wireshark the DHCP offers show the IP address of the Dell Core switch and not the actual DHCP server.