Looks like the download page is getting hammered. FWIW, the download buttons on the big white panels didn't work for me. If you scroll further down the page to the list of all downloads, that worked.
Piss-poor caching mechanism that can't spit out static frontpages with relative ease. Still getting 504's.
https://aka.ms/vs/15/release/vs_Community.exe https://aka.ms/vs/15/release/vs_Enterprise.exe https://aka.ms/vs/15/release/vs_Professional.exe https://aka.ms/vs/15/release/vs_TestProfessional.exe