Gerrit "partially" logs me out overnight. When in this state I can still navigate the site, see my review requests, write comments on reviews etc. However upon clicking the review button a "Session Expired" error dialog appears. After signing in any draft comments are forgotten, causing loss of work / data.

Either the session should not expire so quickly or the "Session Expired" error should be presented sooner. Given that the site requires an account I wouldn't expect any part of the site to be accessible once the session expires.