Rosette was out to catch Aeric in the act and possibly ruin his disguise and his lie. However, the Prince of Starlight had one thing in his favor.
Aeric's Dungeon was irregular, and Lobby Progression within it operated differently compared to regular Dungeons. While his team faced those grueling spikes of difficulties in their Lobbies, other groups in standard Dungeons progressed more steadily.
So the only way the girls could ever get to him was if Aeric's team remained suspended in the Lobby for way too long. But even with that, catching up to them was difficult, especially because they were different types of Dungeons - regular and irregular.
But it wasn't impossible.