I was having similar issues that turned out to be a pre-configured alert with an action to email an invalid e-mail address. This was causing the Information Service to hang and producing the same type of errors when viewing the SolarWinds webpage I could see other resources like NPM, NTA, APM but not NCM resources.
Try to disable all your alerts and see if the issue goes away. Someone from support would know the exact alert name I cannot remember what it was.