After the upgrade to 1803, IIS AppPools are not started since the Windows Process Activation Service is not running. Attempting to start it and it stops within a few seconds.
Event Viewer shows:
ID 5215: The Windows Process Activation Service (WAS) failed to execute initialization for offline setup. The data field contains the error number. (80070002)
ID 5005: Windows Process Activation Service (WAS) is stopping because it encountered an error. The data field contains the error number. (80070002)
ID 7023: The Windows Process Activation Service service terminated with the following error: The system cannot find the file specified.
I tried uninstalling/reinstalling IIS and WAS through Windows Features - \Windows\iis.log does not show any issue. Machine keys seem ok. applicationHost.config is at its default state. \inetpub\temp\appPools looks OK and is empty.
I ran procmon to try to see if anything of interest showed while attempting to restart WAS but there is no indication of what file it is unable to access prior to termination.