Where to start?

  I guess with dot1x you have to authenticate before the dhcp request is allowed to go to the server.
  

CLI on ISE Nodes
show ports | in 8443
show application status ise

Lets have a look at what a device is doing on the switch:
show ip device tracking all
Show auth sessions
show ip access-lists
show aa servers

ISE Portal Issue
ISE CTS Issue