On boundary group for branch office i am not add primary server for site system server. i want to deploy windows updates from DP.
If you have not selected the option for content download through MS Update Cloud and you have the correct boundary configured, content download will always occur from local DP only.
I understand, you don't want to add Site Server in your BG. It will anyway try to download through Local DP only. Here we need to understand what is the error showing in WUA Handler log in client.
On Site Server Open, IIS Manager Console >> Check if WSUS is in Start State or stopped, if stopped start and check if that also resolves the issue or not.
On one of the client machine, try to perform below troubleshooting and check if that helps in resolving the issues:-
>> Stop and Disable Windows update Agent Service
>> Regedit >> HKLM>> Software >> Policies >> Windows >> Windows Update (Delete this Folder key).
>> Start the Windows Update Agent Service
>> Run Machine Policy retrieval and Software update Cycles from Actions tab.
After that monitor the logs and check if you are getting the error or not.