HELP! First set of true leaves yellowing

[Alexflme]

In the last week the bottom pair of true leaves has been yellowing randomly. It's been a fairly slowly.

I'm growing in soil, feeding organic nutes and she's been thriving. She's a small, autoflowering,outdoor grow, in a 1.5-2L pot I'm about 1.5 weeks into flowering (31 days overall from sprouting) and everything else looks healthy. All leaves are nice and green from the top to the bottom, from the new growth to the old, except that first pair (Apart from a few insect bites here and there). Overall no deficiency signs everywhere else.

My question is what could be happening, and if I should just leave the leaves alone or trim them off.

Here's an image of one of the leaves. Thank you in advance!

[CaptainWiese91]

1,5-2 L por is way too small.
it’s getting root bound in my opinion.
what is your PH levels ?
what kind of soil are you using ?
And how long have you giving nutes? And what ratio of the NPK