As in, you sat in the chair to wait for nighttime past curfew and you can't enter the common room again, or is this related to the ball party quest? First time I've seen this bug, sorry! And it's an AnyPastel mix together with different loras as needed for different characters
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If the ball party quest is active still, you need to talk to a girl in the middle of the floor in the upper part of the ballroom. It's also skippable by simply talking to the Gryffindors in the same area, and then doing the part with Hermione.
If the ballparty is finished, there's definitely a bug here