That looks less like a mystery disease and more like the plant is pulling mobile nutrients out of the oldest leaves now that the auto has kicked into flower.

Top growth still looks fairly green, so I wouldn’t panic or start dumping a bunch of stuff on it. But at 4-5 weeks on an auto, yellow lower fans usually points to the soil not keeping up with demand, especially nitrogen and general mineral availability. Same thing happens with tomatoes when the root zone is a little underfed or watering has slowed the biology down.

I’d want to know what soil you’re in, what you’ve fed so far, and how often you water. If it’s just bag soil and plain water, I’d do a gentle top dress with worm castings/compost and a mild organic dry amendment, then water it in slowly. Don’t try to make those yellow leaves green again, they’re spent.

Also if that pot is clear/translucent, I’d slide it inside an opaque bucket or wrap it. Roots and rhizosphere life don’t really want light on them.

I heard you on the vid
Autos will flower by age & stress can easily tigger early flowering however a auto flowering at week 4 is normal
Auto’s normaly start flowering week 3-4 albeit the odd strain goes maybe as long as 7 weeks before flowering. that it is flowering at week 4 is normal
I would agree with @compostmike need to know a bit more
Could be your watering schedule or as said a nute issue

Vegasnative said:

I'm growing two autoflower strains and the bottom fan leaves have turned completely yellow..I will post some recent pics if anyone could tell me what most likely the problem is that would be super helpful! Thank you!

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Yo dudes sound like cheechs and Chong on the video the soil looks pretty dry from the pics. Is possibly a slight nitrogen deficiency from under watering. Is best to saturate the full pot when watering.