Using the most current version of Notepad++, I experienced a reproducible behaviour when converting a big file from UNIX/ANSI to UNIX/UTF-8 (using Encoding->Convert to UTF-8). I played a bit with the size: Initially, the file was about 13M in size. Using successive approximation, I narrowed the file size to around 5m (5147748 bytes). Below this, the conversion works. Beyond this size, I have an empty file after the conversion.