I’ve had meetings specifically for team A’s problems. Team B gets invited to assist. Within ten minutes the meeting was all about team B and none of team A’s problems were solved. “Team B” is notorious for hijacking meetings. I’m not a psychologist. I don’t feel qualified to speculate about WHY they do this...

If Team B is completely going off-topic, stop them and say that you'll need to schedule a later meeting for that discussion. I'd say that's a polite and reasonable approach. They might even start to back down a bit if they catch the hint. Always try to relate the discussion (derailment from B) back to Team A's original 'ask', or ask Team A what they think of 'Topic from B' in relation to their problem. If Team B is talking about stuff completely unrelated to their jobs, keep asking Team A for context and ask Team B what they think of what Team A just said. You gotta keep pushing them, and you can do it politely. (that being said, this stuff gets way under my skin)

Do you have a Scrum master? If not try the “lean coffee” style of meetings.