It could be that you have a corrupt Windows Index. You can rebuild it by the following steps:
To rebuild the Windows Search index, head back to Control Panel > Indexing Options. Click the Advanced button and make sure you’re on the Index Settings tab of the Advanced Options window.
Under the Troubleshooting section of the Advanced Options window, find and click the Rebuild button. Windows will warn you, just as we did above, that the index rebuilding process may take a long time, and that you may not have full search functionality until it’s complete. Click OK to accept the warning and start the re-indexing process. (Source: https://www.tekrevue.com/tip/how-to-solve-windows-search-issues-index-rebuild/)
I'm also pretty sure that you don't need your Windows Indexer turned on if you are using Everythings index to search your files. In this case, you should turn it off.
Cheers, Eric (Full disclosure: I work for the developers of Lookeen Search