Since when are you having this issue? Do you get any error messages? Have you tried working on a different recommended browser (Edge, Chrome, Safari, or Firefox) or after clearing the cache/cookies of the browser you're working on?
Such issues generally get resolved by restarting the browser, logging out & back in, or clearing its cache/cookies.
Do you see an error message while you're downloading your project? What type of project is it? Is it a template or your own? What is the file format you choose for the download? Is it happening with every project?
Some workarounds might help:
- Test in incognito or privacy mode
- Clear the cache/cookies from the browser
- Use a different browser such as Google, Safari or Microsoft Edge
Before attempting these steps, closing the previously opened pages is recommended. If the issue persists, share a screenshot while you trying to download the files.