Leaves are turning yellow and dieing. Looks just like nitrogen deficiency. I'm in early flower

Yes I have noticed this happens more in outdoor grows and it’s quite normal and not as concerning as if you had yellowing dying leaves in and indoor set up. Several of my outdoor plants have started with some yellowing a dropping a few leaves also. I don’t believe WPM would have anything to do with this.. I also realized I was likely underfeeding a bit as you mentioned.. I’ve got some big girls outside and wasn’t used to their nutrient needs. That said I wouldn’t go slamming it with nitrogen - seeing ass your flowering has begun. Maybe up your source of N for one feed then go back to your normal feeding schedule!