Deja vu may occur when there's a delay in information processing between brain regions.

One theory suggests déjà vu happens when the brain’s familiarity system fires without a matching memory, possibly due to timing mismatches between perception and memory circuits. Episodes are common—many people experience it a few times per year—and can be more frequent with stress or fatigue. It’s still not fully settled science, but timing/processing hypotheses fit the “I’ve been here” feeling.