Coming here to just say I've been dealing with this same issue and that the fix stating to quit the Box Edit program completely works! Thank you to Daniel for figuring this out and posting the solution.

Same here. Wondering this for ages. Thanks for those useful solutions in all previous comment.

If the above solutions don't work for you, I also had success with the first response here: https://support.box.com/hc/en-us/community/posts/9597952583699-Box-Drive-not-downloading-Files

Quitting Box Edit from the system tray works for me too. This has been so annoying, at least there is a workaround.

To anyone following this thread. If you haven’t had success with the other mentioned solutions welcome to the club. I found the issue was a very simple fix.. file pathway is too long. The more folders deep your file is and the longer the name on said files will eventually cause an issue where the file won’t open and might even cause the box folder to close when you try to open the file. Simple shorten the pathway. Use less sub folders.