I think it's fairly well established that voiced stops tend to depress f0 while unvoiced stops tend to raise it, but I'm less clear on other types of consonant. I'm especially interested in sonorant consonants and semivowels, and whether they have any systematic effect on the f0 of the following vowel. More specifically, is there any reason why initial [j] should depress the f0 of the following vowel?
You tag this as a phonology question but refer to effect on F0, which is confusing. There are substantive factors in the phonetics which contribute to raising and lowering of F0, but there are also categorial phonological rules involving that change from one tone category to another. I assume that you are talking about continuous F0 effects in phonetics and not phonological tone effects. Sonorant effects in phonology are known, and have a range of historical explanations.
Especially if this only involves [j], that would be very surprising and unexpected, so well worth firmly establishing. There are also vowel height effects where [i,u] have higher intrinsic F0 effects, and if the corpus has no cases of [w] then this could be the reason. The effect has long been known for high vowels but I think it has not been systematically studied for glides since the effect would be harder to measure (you can sompare [i,u] to [e,o] but what do you compare [j,w] to?).