If they’re nicer to you in DMs than in public, ask yourself why.

Private warmth and public distance is a combination worth examining. Somebody who is affectionate in messages and cool in a corridor is managing two audiences, and you are the one being kept off the record. The reason might be shyness, or a group they are afraid of, or something less flattering about how they rank you. None of those are things you can guess from the outside.

Ask them directly, once, without an accusation in it. Say you have noticed the difference and you are curious about it. The answer, or the refusal to give one, will tell you most of what you need.