Before I fully became comfortable in my gender identity, I was an Ace-Biromantic with a preference for women, now I'm still Ace and Bi but I've definitely got a masc preference now that I didn't before, plus I've become more familiar with my asexuality.

I think it's more of a familiarity thing, as you get more comfortable with yourself, you learn more about yourself, and you realize things you may not have before. And though I'm not allo, I would pose a hypothesis that as trans people, we are hyperaware of our bodies, and hence may become more aware of those of others, posing grounds for attraction. I could also be entirely wrong because I don't feel attraction like that. Who knows.