Trying to upload hundreds of files eventually result in a "[400] invalid_grant - Current date/time MUST be before the expiration date/time listed in the 'exp' claim"

Hello,

Using the Java SDK I've been having an issue when trying to upload a large amount of files (ranging from 5MB to 50MB for each file). My process will start fine and perform without an issue up until a certain point where I will eventually get a error 400: invalid_grant - Current date/time MUST be before the expiration date/time listed in the 'exp' claim.

I'm communicating with Box using a private/pub key. My Unix server has the correct time (ntp is configured correctly). And more importantly it only happens when trying to upload hundreds of files at once. If I leave my program running for a week let's say, and try to upload a single file it will work (so it's not a natural clock drift happening on the server side). 

I'm using Box 3.8.0. Any idea how to resolve this? Is Box suited for such large uploads? 

Thanks,