Since I installed cloudflare users can’t download PDFs from my site, when you click download it says ‘Failed - Server problem’. They can do it using a workaround by clicking print and the ‘save as pdf’ but not ideal.
Strangely it doesn’t seem to be a problem in Mozilla Firefox but it is in Google Chrome and Edge.
I wouldn’t expect it to be a Cloudflare caching issue. You’d have to use your browser’s Dev Tools (F12 in Chrome) to look at all the headers for that URL while logged in, and not logged in, then compare them.