https://support.microsoft.com/en-us/topic/kb4511608-fix-full-text-search-fails-to-remove-files-from-ftdata-filterdata-subfolder-in-sql-server-2014-e765aecc-b427-7084-e907-dc69cb8555aa
KB4511608 - FIX: Full-text search fails to remove files from \FTDATA\FilterData subfolder in SQL...
FIX: Full-text search fails to remove files from \FTDATA\FilterData subfolder in SQL Server 2014