We have an on-premises SharePoint 2016 farm consisting of 3 servers (application&search+wfe+database). We recently found that the enterprise search wasn't working. When looked at the crawl logs under the Search Service Application, the following error was reported and the crawl wasn't working:
Content Processing Pipeline Failed to Process the Item
There were comments on Internet suggesting that this could be due to an issue with Manged Matadata Property Mappings, but when click on the Search Schema in Search Administration, it displays the following error without showing the Managed Properties.
An unknown error occurred.
We've tried restarting the Search Host Service and Time Service, but it didn't help.
Any assistance with resolving the issue is much appreciated.