
generally it’s more about which one is -sexual and which one is -romantic. just “pansexual” implies they’re also panromantic, but with dual labels (like pansexual lesbian), “pansexual” refers exclusively to sexual attraction. “lesbian” isnt -sexual or -romantic, so it refers to whichever attraction isnt specified (in this case, romantic attraction)
I think it really depends since “a pansexual gay” sounds worse than the other way, but “pansexual lesbian” sounds better. it probs has to do with which our brain considers “more” of an adjective. “gay” is always an adjective, “lesbian”is often a noun, and “pansexual” can be either