One hole will not grow

I have one spot in my unit in which nothing will grow. I have tried different types of lettuce and still nothing sprouts, only in that space. What could be causing this?

Make sure to check if the issue with the cup, or wick. Is there water coming through and the soil is moist?
Try to put another plastic cup in that spot, for example, to test the cup.
Changing or cleaning the wick can also help.

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