Looking at your diary, you switched to early from Veg nutrients to Bloom nutrients.
You must keep Nitrogen high enough during the first 3 weeks of 12/12 cycle, to support the stretch.
What is happening is called a "Die-Back", it happens after the stretch when the plant didn’t get enough Nitrogen during this stage of the growth. The plant is moving its nitrogen mostly from the bottom to save the top.
Unfortunately there’s not much you can do about it at this stage. Adding Nitrogen will be useless, the roots are processing Phosphorus and Potassium from now on.
Do not unplug the yellowing leaves and let the plant do its own job.