I have set up a new tune in 3/4 time but a redline appeared under each of the bar numbers and the song was only playing 1 beat per bar

With dumb luck I did a few things and it is now playing 3 beats per bar but the redline is still there

So I have 2 questions...
1) What does the redline mean and how do I control it (clicking on it does not present an option to clear it)?
2) Why and how did it switch to one beat per bar while my time signature was 3/4?

Any help would be appreciated