They do that often when the plants dont have enoeugh of what they need when they are budding so they eat the leaf

another thing is maybe some Vit B man or dilute some urine
Its what id do but yeah the yellowing happens often ive notticed like if the dirt is pretty used up or when you dont feed em before ur buddin and the dirt doesnt have everything they needed or just nature lettin you know that ur plants are almost done and its time to harvest replicating harvest time aint we?