My apologies for the delayed response, much of the team has been out during the OpenStack conference.
We have been seeing more intermittent 500 errors than we'd like. We are working on adding capacity to the cluster which will help alleviate those. Be on the lookout for some maintenance windows in the coming weeks that will signal the beginning of this process.
Have you created a support ticket with details on this? I'd be interested to know what client or library you're using to upload those files. Please include the dates and times so we can investigate in the logs.