Hello,
WPM is using own local user accounts for playback. Is there any chance that some network settings are applied on domain account level through GPO? WPM accounts are not affected by user-level GPO.
Fact that it sometimes work and sometimes not looks strange but can be caused by different runs using different WPM account (there are 7 on standalone Player). Do you have multiple playback locations and does it fail on all of them? Can you try to stop "SolarWinds WPM Player" service, go to user management in Windows, delete all SEUM-User-# accounts and start "SolarWinds WPM Player" service again?
Another option worth trying may be to use domain accounts for players. If you go to "c:\Program Files (x86)\SolarWinds\Orion\SEUM" there is "SolarWinds.SEUM.AgentDomainConfigurationTool.exe". Run this tool, enable domain accounts and enter credentials for as many accounts that it asks for (2 or 7, based on where Player is installed). Each account on single machine has to be unique but you can use same set of accounts across different machines. It's good practice to create extra accounts just for WPM, it's not recommended to use accounts of real users.Save settings and see if it helps.