Unity 2019.1, 2018.3, 2017.4 ALL failing to connect to package manager server

This issue, as experienced by multiple other people in the community, starting all the way in 2016 has still not being fixed, and occurs to me at least every couple months - this greatly impacts my development ability, and I'm sure it does so for multiple people. The hotfixes released by unity do not solve the issue, nor do different versions of unity, so this must be a hub issue.

What I've tried so far:

• noproxy
  
  
• disabling firewall
  
  
• whitelisting/ disabling windows defender
  
  
• testing ports
  
  
• run as admin
  
  
• uninstall ALL unity versions AND unity hub
  
  
• install patches

I hope unity addresses this issue soon, as the only other option currently is switching over to unreal

edit: I have realised it's possible to open unity with "-noUpm" cmd argument, however that creates all sorts of issues, and is not a great long term solution, as there is no way to pass cmd arguments through unity hub

 

I have the same problem, in unity 2019,2018.3,the package manager can't load the preview manager,and shows "loading packages" in the left bottom all long.
I try to add package from disk and there's an error.
btw,sometimes it can work in 2018.2.2,sometimes doesn't.