If you see a yellow alert warning symbol on any thumbnail images in your Document List, this indicates that the PDF file may have performance issues, may be corrupt, or may cause the app to crash when searched.
If you are experiencing any issues when searching the OCR data in a Case File it may be due to these files. You may want to move these files to a folder at the topmost hierarchal level in the case, and then perform any searches once inside specific folders at a lower hierarchical level.