While attempting to login to the NBU administration console, the following error is observed: Unable to get data for client from server (Status 25)

Troubleshooting steps
1. Disable Win2019 UAC follow link https://asvignesh.in/disabling-uac-on-the-windows-server-2019/
2. Verify the masterserver is correctly configured with IP address and hostname
C:\Program Files\Veritas\NetBackup\bin\admincmd>bptestbpcd -verbose -debug
That error about the hostname+dns suffix namd is not allow to authorized hostname server
3. ipconfig /all for seen Connect-specific DNS suffix as “falconstor.net”
4. Open Network & Internet settings -> Ethernet -> Change adapter options -> Ethernet0 -> Properties -> Internet Protocol Version 4(TCP/IPv4) -> Advanced -> DNS -> Append the DNS suffixes (in order): there is empty field.
5. C:\wmic path Win32_NetworkAdapterConfiguration get caption, DNSDomainSuffixSearchOrder that return have string “falconstor.net”

Resolve steps
Try to remove “Connect-specific DNS suffix” string “falconstor.net”
1. Launch Registry Editor -> Find “falconstor.net” that will be in
Computer\HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\Tcpip\Parameters\interfaces\{xxx-xxx-xxx-xxx-xxxx}\DhcpDomainSearchList

Root cause reason:
The Windows2019 been set “Connect-specific DNS suffix” from DHCP server provided.

Refer link
https://superuser.com/questions/868979/windows-remembers-old-dns-suffix
https://www.veritas.com/support/en_US/article.100034238