Unable to view folder containing the pound sign / hash sign in Bitbucket web interface

When I open a URL like this:

https://bitbucket.org/MY_COMPANY/MY_REPOSITORY/src/master/src/C#/

I get an error message in the browser:

Hmm... can't find that one

That file or directory doesn’t exist. Go back to the previous page and try another one.

The header of the page is showing the folder name as "C" instead of "C#", which could be related to the issue.

I have the "New source browser experience" enabled in Bitbucket Labs settings.