My project did this. I found it was my automation lanes that went out beyond the song end. I am not sure how I did this. And I found it quite hard to trim or delete the extra bits. Click the "Transport" so start/stop/record etc windows pops up. Under the record button, there is a "go to the end" button (its a button that has a right pointing arrow & then vertical line). This will take you to where your project thinks the end it. You will find there is something between the end of the song & this point. Individually delete bits or set left & right markers & delete the whole section. Click "delete special" & select all options. If you have an "end" marker, that will get deleted too. And I found I had to do this to get it to work. Then just add that marker back in. This fixed my problem. But 1) I don't know how I did it in the first place (I'll put it down to user error), & 2) I found I couldn't "split" an automation lane, & 3) even when I delete nodes, there was still an ongoing dotted line where they used to be.