I have seen this issue from other posters a lot, but like Alistu said I don’t think the file attaching has ever not worked for me. I understand the frustration but since we cannot reproduce the error it is very hard to fix!
Do you know if it happens only to some file types? It could be possible that the university network you are on blocks some file types for uploading/downloading. I would suggest that you both try attaching files from a different network as well and see if you get the same problem.
Note: I just saw that you both are part of the same university “North Eastern Hill University” which might point to the university network being an issue.
Regards