

Brown crack in ceiling
I have this 24 inch brown line on my first floor ceiling. I marked it last year and it has grown about 8 inches over the past year.
Whats up with this? How do I fix it?
I thought it was water damage but it is not below a water source. I’ve included a picture of the area directly above it. The second floor air duct runs right over the crack. Is it possible I’m getting condensation on the 2nd floor duct and it’s causing water damage?