That sounds like one of my trips. Without fail something goes awry every time we visit Germany. It's one of the reasons I go out of my way to eliminate layovers and try and simplify literally everything. Sometimes there's just nothing you can do, though. Glad you made it back and hopefully United will make things right. One issue I've had with US carriers in Europe in general is that they don't start the check-in process quickly enough. The crew doesn't typically show up until right at 2-hours prior to departure. Since there aren't that many flights, the ticketing team is usually just the flight crew. If something doesn't line-up (or if the security lines are excessive), there is almost no time to do anything about it. Domestically I'm one of those people that rolls up 3+ hours early, but it has served me well.