We started using the session capability of the android tracker.
We do not see the following fields getting any data, like it does for our web tracker:
domain_userid, domain_sessionidx, and domain_sessionid
Instead all of the data is going to com_snowplowanalytics_snowplow_client_session_1
This is correct behaviour for the Android tracker.
Currently there is indeed a difference between the JS web tracker and the mobile trackers (the web tracker populates the fields you mention) and this will be changed in a future release so that all trackers populate the new context.
When we release this update, we will provide upgrade scripts to move historical JS Tracker session data into the new context.