Upload fails for filename with '+' in

When I try to upload a file with a ‘+’ symbol in the filename, the upload fails. In the uploader it shows as below:
In the browser console there are a number of 403 errors. Renaming the file without the ‘+’ allows it to be uploaded.


Do you have any logs on Cells mentioning the error?

There are no entries in the server logs from uploading it. The only errors I see are the above screenshot and this from devtools:

Hello, do you have an Apache proxy in front of Cells?