Answer
This happens due to unstable or incorrect keys, causing React to reuse DOM nodes incorrectly during rapid updates.
Quick Answer
This typically happens when keys aren't stable — React creates a new component instance instead of updating the existing one, momentarily showing both (old unmounting, new mounting). It can also happen with concurrent rendering where React renders multiple versions of the tree. Stable, unique keys are the primary fix.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ