Why is this girl so dry to only me?

So basically there is a girl in my school where her behavior around me is so dry compared to everyone else she talks to, no matter girl or guy. I know this because when I see her with her other friends in my classes she seems normal. But with me, she’s so dry and almost seems like she is completely disinterested and annoyed at me. I don’t understand because I haven’t done anything that would make her mad / uncomfortable and we’ve known each other for a few months now. It’s like every time we talk , she seems like she wants to leave. Like even smaller things like the way she greets me is different and seems so much more dry and cold. Like when she sees me she says hi and starts walking with me but like she seems like she doesn’t want to talk anymore, it’s so weird. I started becoming more dry to her because I have been trying to brighten up the conversation everytime we talked but it won’t work.
Why is this girl so dry to only me?
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