I had a similar issue last grow. Gorilla Glue Auto in amended organic soil fed PH’d water. All was going well until mid flower when suddenly started getting yellowing leaves, eventually falling off, slowly one by one. Ph in and run off were spot on. Tried giving it nutes and basic supplements but nothing seemed to stop the deterioration. Eventually, light PH’d feed was enough to limp it home. Got a decent harvest given the circumstances. By the end, only bud leaves were left on the plant