Strange yellowing leaf in flowering

Hi That very bright new growth, I usually associate with iron deficiency. Especially since it's starting bright and then growing out to be green and healthy looking. That's usually the main sign that its happening at a low rate...not usually catastrophic. If you're not using a calmag supplement (which usually has iron also) you may want to do a feeding once a week. Also double check your ph as that can usually be a trigger..especially from higher ph like 7. I sometimes double check and recalibrate my ph pens as I've had them lose their accuracy over time. Happy growing.