I can't see other players' skin on any server

Why can't I see other players' skins on some servers? I have disabled “only allow trusted skin” option but the result is still the same. I can't see all other players' skins on the Hive server and CubeCraft server, but I can only see 1 to 2 other players' skins on the Lifeboat server at a time. Attachments are below. The bottom attachment is the Lifeboat server I saw only one player skin successfully loaded.