Good ol green crack am i rite :). One of the most commercial strains pre-recreational legalization.
Ok so depending on your phenotype, green crack will almost always throw out yellow leaves as it cannabalizes itself for extra nutrients. However if your yellowing is isolated to a single branch, there are a couple possibilities. Most commonly this occurred for me on plants that had branches that didn’t have Union joints, and that got a large portion of their nutrient supply cut off as the main stem grew and pinched off the side branch. If your branch doesn’t have a nice U shape where it meets your main stem, and instead has a V shape, it may be getting pinched off. This happens with lower branches on seedlings a lot. Sometimes those V union branches are during inside and develop fungal infections that lock out your branch. Once that happens the plant tries to drain whatever nutes it can from available sources, which are your leaves.
Below are pics of a good Union and a bad one. The bad ones will get pinched off sometimes and leave your branch starving