Client fails to download TFTP, Event 4101 (MDT, WDS, DHCP and IP-Helper)
Operating systems affected: Windows Server 2016 (Monthly CU 2019/03 KB:
KB4489889) and Windows Server 2019 (Monthly CU 2019/04 KB4493509)
Solution: uncheck the setting “Enable Variable Window Extension” on the WDS-server.
Go to Windows Deployment Services > Servers > Right click the server name and then choose Properties. The setting is found under “TFTP” as can be seen below: