I've never seen this before, can you please open support ticket for this case? It would allow us to investigate log files and better understand why it happens.
This issue can be resolved by rebuilding the website on the Orion server using the following steps:
1. Ensure that you are logged on as a Local Administrator and that UAC is turned off.
2. In Internet Information Services (IIS) Manager, delete the SolarWinds NetPerfmon in Sites and SolarWinds Orion Application Pool in Applications Pools.
3. Change the C:\inetpub\SolarWinds\ folder to "SolarWinds_old"
4. Run the Configuration Wizard found in [Start -> SolarWinds Orion -> Configuration and Autodiscovery] and ensure that you have checked off the "Website" option and that all settings are in their preferred state (bindings, authentication, etc.) You may skip the Website Optimization if you wish, this will save you quite a bit of time but it would be preferable to run the optimization if installation if time is not a priority.
Thank you for bringing this to our attention @cm_jamesriggs!