This is still an issue in 2019.
This is definitely a bug. Filenames/browsers should not have any effect on whether users can download or not.
For the record, I’m using Chrome, and I’m attempting to download small files with simple names; there is absolutely no reason in this case why Fiverr downloads should fail. I am able to download successfully from other websites (Google Docs, Dropbox, etc etc etc).
This is a bug in the Fiverr platform which should be fixed.