Server.app "SSLProtocol: Illegal protocol 'TLSv1.2'"
This looks like a mismatch between the version of Server, where the apache config resides, and the version of apache which is delivered by the OS. 

Look at the .conf files in /Library/Server/Web/Config/Proxy/ and replace any instances of TLSv1.2 with TLSv1.

You may also need to do that with some of the other config files included by those files.

That said, since both pieces look to be prerelease, you should review your seeding agreement, it may have info on a better place to ask this sort of question.