At the "Publish" step, if we click on "record more files", nothing happen.
Actually I just tried using Firefox 66.0 on Mageia Linux 64-bits and it worked. So it seems the problem occur sometimes, probably on some webbrowsers.
Problem occurs on Firefox 66 on Ubuntu 64bit – so it's apparently not due to browser-version. Maybe an Addon? I'll try out next time.
I can reproduce the bug in Firefox 70.0.1 (64-bit) on MacOS Mojave 10.14.6.