In the Quickstarts, the new auth0-spa-js SDK does the silent authentication automatically. I suggest you try it out with a database user first (not via social connection). If that works, then it’s obviously the dev keys used for the social connections causing the problem (as it’s the case in the many other threads on this topic in the forum).
IIRC, whether it works with dev keys or not also depends on whether you’re using the Classic Login Page or the New Universal Login Page (ULP).
How to get your own keys for Google, Facebook, etc. is descibed in the docs linked in the settings dialog of each connection:
For Google for example: