I have a few notes that I edit on all kinds of machines, but mostly on Win. They may well be dos formatted. Some of the files will be displayed, some not. Not sure how to fix that. I am wondering if this issue is related to the format (dos/Linux)? Maybe there is a known fix? Server runs raspian.
Afaik, the file type recognition does normally not use the file extension to identify files but the mime type. You should check the mime type of the file on the console to identify the root cause of the problem.
file --mime <file>