Sometimes you find clients are failed to download software updates , application and you will be seeing error massage HTTP code 503 service unavailable in few client logs.
First you have to check the boundary and boundary group are correctly configured
Then check if you see any error in IIS or check the application pool is running, If its stopped start again.
If the IIS Application Pool stops frequently, check for any error in event viewer
If you find the about error, it could be related with permission issue
Check HKLM\Software\Microsoft\SMS permission, if the permission are not configured for users,
Create it as mention below.
