Nute Burn or something Else?

looks like light burn to me - interveinal, but expands down center of blade. It often won't heal. Consider recent behaviour, but leaves look fine eslewhere. just top impacted. although i'd expect more droop in leaves. Raise lights if you can. possibly trace elements, which if in soil would be odd and more likely pH related. Ensure you are 6.8 in soil and cross that off list. 6.5 soilless, which again very odd as your nutes would assuredly provide it... same with hydro and what.. 5.8? not a hydro-guy, here.