This happens as soon as I take my eyes off you with 目を離す

Idiom Explanation: Averting one's attention with 目を離す

During a trip on a train, Conan accidentally overhears that there is a bomb on the train, and it’s set to go off. Conan tries to follow the criminals as they disembark, but Ran stops him at the exit door.

コナン:: 「あーーー」; “Ah...!”
蘭(らん):: 「もぉ！目(め)を離(はな)すとすぐこれなんだから！」; “Geez! As soon as I take my eyes off you, this happens!”

Key Points

1目(め)を離(はな)す = to take one’s eyes off someone

In this scene it means Ran stopped watching Conan closely for a moment.
The idiom is about losing visual attention, not literally removing your eyes.

2〜と marks a regular consequence

「目(め)を離(はな)すとすぐこれ」 means “as soon as I take my eyes off you, this happens right away”.
〜と often presents something as the natural or repeated result of the first action.

3これ points to the trouble in front of her

これ does not name the problem directly.
It works like “this mess again”, relying on the immediate situation for meaning.