Late in flowering stage it's common to see either the ph drop as the buffers in your soil fade, or rootbound issues. Mild cases of either will cause the claw, but rootbound won't create a nutrient lockout condition like ph drop will.

When rootbound, water just flows through medium to the drip tray with virtually no absorption. This means the plant cant hydrate nor can it uptake nutrients.
Moderate ph drop will create a nutrient lock-out condition starving and yellowing the plant.

I always transplant into final pot about 2 weeks into 12/12. This avoids both issues unless it's a long-flowering sativa.

Without you filling-out the troubleshooting form, this is just a guess. But I'm very doubtful it's a nutrient thing as you mentioned. The Bushmaster may well contribute to root growth, but is likely not the cause of the claw per-se.