Hi .appear to be PH variations. it may also be some extra heat and lack of ventilation but I am more inclined towards the PH. they also seem to be in need of calmag, and you have applied a source of calcium and magnesium to it. good luck mate
@Fuanarchy Hi there I hope you are well
Is the plant that has burnt leaves directly under the grow light? Looks to me to be heat related maybe a hot spot that isnt getting fresh air