This would be more likely if Leilei cannot use magic when she's on our world as the intercepting dimensions there might be different.
It's likely appearing in a different way on the other side, as the past chapters did say from the professors that there are alot of irregularities happening on Earth (wrong star aligments, earthquakes being more common etc...)My theory is that the darkness is the region outside of both worlds that is exposed due to the distortion the world, however it would not explain why that only exists in the SR but not our world.