Hakyeon confrimed that he did talk to Minhyun in the conservatory. He said that he tried to get Minhyun to come to the party with him, but Minhyun stormed out and Hakyeon hadn't seen him since.
Mrs. Peacock finds Jungkook suspicious because "he just seemed too concerned about Mr. Boddy. Like no one has ever been that concerned for him before."
The only rooms that were locked were the upstairs room, but since the event was happening that is pretty normal.
(Upstairs rooms are the bedrooms, the billiard room, observatory and the theater.)