Lacuna

Lacuna: A lacuna is a gap or a missing part, most often used metamorphically for an intellectual blind spot, a gap in intelligence, or missing information. Lacuna (the word) is already a metaphor and shares its etymology with lake and lagoon.

Besides, how long was this odd lacuna of inactivity going to last?

It was like kernels of crop beginning to pop. first slowly, with lacunae, and then in a solid mass.

A Book for Today: Admission by Jean Hanff Korelitz ***

Scientists hit a black box, a lacuna in knowledge they can't describe despite understanding more or less what fed into and what evolved out of it.