Early autoflower yellowing (Week 5 to 6)

Looks to me as if you have a slight N toxicity. You're right around the stage where she doesn't need much N at all so she could be getting burned by leftovers in the soil. In this case, make sure you've lowered the N in your feed and just keep going as normal until the N level in your soil drops to a proper range. I wouldn't go so far as to flush or anything like that. You may see some more progression for the next week or so before it stops spreading.