The cause can be the lucene engine used for searching is corrupted and you may need to perform additional step to fix it
If the above steps dont help then you need to perform below
1. Pause the "Index contents and documents for search" scheduled job
2. Turn off synchronous indexing in the NSA. NOTE: Make sure you restart
services after doing this.
3. Using CSA add "-Djava.io.tmpdir=c:\javatmp" to app service jvm parameters (unless this parameter is already present and you can set the path based on your operating system)
4. Using CSA add "-Djava.io.tmpdir=c:\javatmp" to bg service jvm parameters (unless this parameter is already present and you can set the path based on your operating system)
5. Search for and delete any files that end in write.lock on your app
server(s).
They will look something like this:
lucene-62db5567fbeaae16396e79fb8fe42895-write.lock
6. Restart app and bg services.
7. Delete the nspider and nspiderfile folders from the file server
8. Log into the app server as someone who has full control of the filestore folders including the ability to create new folders/files like the nspiderfiles folders
9. Run the "admin search recreate-index-data" command
10. Run the "admin search recreate-index-files" command
11. When this has completed, turn on synchronous indexing in the CSA.