There is a problem with the alpha download site. https://dev-builds.libreoffice.org/daily/master/MacOSX-x86_64@49-TDF/current gives a "404 not found". I can't test the software this way.
I can confirm the issue. But it is a infrastructure problem. And for those not Bugzilla but Redmine bugtracker is the correct address. https://redmine.documentfoundation.org/projects/infrastructure/issues/new Or use irc://irc.freenode.net/#tdf-infra to get in contact with infrastructure maintainer.
I have done it for you. It is now ticket https://redmine.documentfoundation.org/issues/2821
The download page has now the correct link. It is https://dev-builds.libreoffice.org/daily/master/MacOSX-x86_64@tb81-TDF/