Hello,
Thank you for posting in Q&A forum.
To further troubleshoot this issue, please kindly try below method:
1.Check if DHCP option 66 and 67 are both configured welland point to the WDS server.
2.Check if UDP Port 69 connection for TFTP is allowed on the server.
3.Check if WDS server has proper permission to access the necessary files and folders.
4.Please try to restart TFTP service and check if it helps.
Hope this answer can help you well.
Best regards,
Jill Zhou