The file manager in the control panel is incomplete

Eh, what?

One thing to watch out for is file encoding. Our servers, file managers, etc. assume that all files are UTF-8 encoded. Especially if you’re on Windows and/or the file is in a language that contains many non-latin characters, you have to make sure the file encoding is correct.

Or someone is hijacking your FTP connection and corrupting the data, of course. Which is a plausible risk if you disable TLS for FTP.