Being brought back to do another interview is not a good sign at Google. Best case is your interviewers totally forgot to cover something important, but more commonly it means somebody has serious doubts about something and they need to check it again.

Or that you're being considered for a similar job but under a different hiring manager.

Another thing to note about Google hiring is that it's very different for different role types. Specifically, for SWEs, Sales, and other roles that are expected to function in a largely boilerplate manner, it's fairly cut & dried how things work, but for roles that are less clearly defined (for example, "program manager" or "solutions consultant") the actual responsibilities can be so highly variable (or so niche) that interviewing for them is a specialization in itself. These kind of one-off situations is where Google's "automate all the things" general mentality falls apart.