sir_isOanswered grow question 4 years ago Might be calcium, phosphor and sulphur related (especially at that stage) as the phosphor and shit is heavily used then. All of that can be related to yellowing.
I'd maybe try bit of epsom salts, some calcium source (calcitic lime tends to be nice for calcium, as it typically has decent sulphur and magnesium too). But yeah, some combo of calcium, magnesium, sulphur. Potentially a bit of citric acid for the medium (as it can help mobilize nutrients).
Another less likely possibility, I've had some really strange shit happen a few times due to root damage if I had to guess, like single branches dying completely, shit like that.
Cheers, good luck dude.