TL;DR Don't use caching for the download urls, and whitelist
/gf-entries-in-excel/* in your caching plugin.
- The downloaded file always contains the same content
- The download link only works once
- The download doesn't work at all
The download link is always returning the current results from the database. Therefor caching these URL's isn't helpful.
Whitelist all download links
Although the plugin returns headers that say the response should not be cached, most caching plugins will think they
know better. But almost every caching plugin has a whitelist. So if you have issues with downloading the file, and you
have a caching plugin; find out how it can whitelist URL's, and add
/gf-entries-in-excel/* to it (assuming it takes
an asterisk (*) as a wildcard).