I noticed what I think was yellow leaf spot. I've treated the plant twice and I hope this won't be giving me any problems further down.
The canopy is now evened out and I'm switching to flower this week.
@heizen, thank you but this grow actually completely went downhill after this point. What I thought was disease was more likely pH issues as my meter was giving wrong readings. I've started a new grow where I kept a flowering clone of this plant tho :)