From [the `/questions` doc][1]:

> ...use the tagged parameter with **a semi-colon delimited** list of tags. This is an **`and` contraint**(sic), **passing tagged=c;java** will return only those questions **with both tags**...

<sup>(Emphasis added)</sup>

If you want questions that have ***either* tag**, use [the `/search` route][2] (or `/search/advanced`).

For example:  
[/2.2/search?tagged=google-docs-api;firebase-database;android-sdk;google-drive-sdk...][3]

As for why the API sometimes differs from the website search, that has been asked a few times both here and elsewhere.  EG, see https://stackapps.com/questions/4459/why-is-there-a-difference-between-questions-and-search-in-api.

But a common reason for API calls that use dates (`fromdate` etc.) to return unexpected results is not [taking into account how the API handles unix epoch time][4].


  [1]: https://api.stackexchange.com/docs/questions
  [2]: https://api.stackexchange.com/docs/search
  [3]: https://api.stackexchange.com/2.2/search?fromdate=1515888000&order=desc&sort=activity&tagged=google-docs-api%3Bfirebase-database%3Bandroid-sdk%3Bgoogle-drive-sdk&site=stackoverflow
  [4]: https://stackapps.com/a/6670/7653