Vertical Dotted Line on Tracks

Hello

Just trying my first mixing.

I am seeing a dotted vertical line running across both my instrumental and vocal track that I am trying to mix together. The problem is that the vocal track to the right of this line is not synchronized with the instrumental track…it is trailing by perhaps half a second. Howe do I synchronize this piece of the track and why is the dotted line appearing in the first place ?

I’ve not seen this problem in quite a while - are you using an old version of Audacity?