upload button disappears

Hi ​@Onset, 

Welcome to Box Community, and we’re here to assist and resolve your upload issue! 

Let's get started with the following information, 

• If you are to upload a single file at time, will the upload button disappear as well? 
• Assuming you are uploading via the Box website, could you upload multiple files via drag & drop? 
• What is the total size of the file you’re uploading? 
• Do you get an error, or just the upload button disappears? 
• What is your permission in the affected folder? 
• Are you able to upload multiple files in your own folder? 

In the meantime, we have listed down the preliminary troubleshooting steps to resolve your upload issue: 

1. Update your browser to date the latest version. Please see this article.
2. Clear your browser’s cache and cookies. 
3. Try another browser
4. Temporarily disabling browser extensions/plugins or ad-blockers that may interfere with Box UI scripts.

Hope it works! Feel free to reply if you need additional assistance.