Yellow level items are not giving proper skill ups. 20 crafts and 0 skill ups. Fix the bug
There are a great number of recipes that display as “yellow” in Classic that have far worse rates of skillup than others, particularly when they are just about to turn “green”. Aside from that nothing gives a guaranteed skillup other than “orange”, it sounds like you got hit with bad rng + one of those recipes. You’d need to add additional data to your post - what profession, what skill level you are, what recipe you were trying…
The way I remember it - and it was probably patched pre 1.12 - we used to get mages to hit us with Intellect buffs because it seemed to allow better chances for skilling up.