hello @jmins , the authentication in terms of dot1x and mab is done at layer 2 hence it's not necessary for the supplicant to have initially an IP address to start the authentication process as the switch will handle the radius session related to the switchport.
The default behavior of a a switchport with dot1x is the following: it will receive EAPol packets to forward the authentication to the server, when the authentication finishes and it's successful, the DHCP, TCP, and more connections will be allowed as it's displayed in this image , for your reference Wired 802.1X Deployment Guide
The ISE or Radius server will update the endpoint with the IP once the supplicant gets/updates the IP with a feature called device-tracking, hence if you want to see accurate IP-MAC relationship in the ISE it's important that you have that feature configured.
Once clarified the last points, I would check the reason of failure of the endpoints authentication failure in the cases you mention, and for the delay in the endpoints authenticated I would place a capture to verify that the DORA process with your DHCP server is completed.
Let me know if it was helpful.
