I use the ObjectiveDropboxOfficial Framework and often get an error 500 when calling batchUploadFiles. It seems to be completely random for which file the batchUpload fails. I call batchUploadFiles for only one file at a time, because it has the convenience to chunk large files, etc. If it is important: the files to be uploaded in this case were all quite small (< 10kb).
Apologies for the delay here. I just wanted to follow up to let you know that the team has been working on improving the error rate here. It may not be possible to completely eliminate all occurrences of issues like this though, so you may wish to implement automatic retrying in your app if you haven't already and you're still seeing these errors.