Would you mind sharing the file, please? I might be able to understand the problem with it if I can take a look.
It'd also help to know the context for where/why you're uploading the file. For example, are you importing a set of usernames for new student accounts? Or is it example training data for a text classifier? Or are you building a corpus for a language model? etc. I'm asking because the code that handles the file uploads is different for each situation, so if I need to fix something, it'd give me a clue what bit to fix.
Kind regards
D