Hi @Anonymous,
Another (perhaps quicker) workaround that you may want to try is to share your project with the other account. This way the other account will have full access to the project and you won't have to download any files. I went ahead and provided steps below that will detail how to Download your project in case this workaround doesn't work in your scenario. You can share the project in A360 by clicking the invite button at the top-right of the page.
Do you think you post some screenshots showing how you went about this process? I just tried on my computer to download an entire project folder from A360 and it worked successfully, so I'm just curious to see what is really going on. The screenshots below show how I downloaded the files as well as the corresponding .zip that was created. Please note that I moved my file (in your case the whole project contents) into a folder so that I only had to download multiple files/folders. I only went ahead and tested one folder in order to save time, but the same concept should apply. After you click "Download" you should see on the top of the screen an orange bar that says "Compressing." When that bar dissapears this will start your download which you will then be able to open the file. As you can see, a .f3z file was created in the folder that I downloaded.


Hopefully this suggestion worked for you and if so, please feel free to mark this answer as a solution. That way everyone can benefit from this thread as well. If you still have more questions, I will be more than happy to keep helping!
Thanks,
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James Youmatz
General Adoption Manager | Informed Design