Looks like this can occur with motion blur off aswell, so likely it's a TAA motion vector issue.

Similar issue occurs in UE5 (see [Link Removed])

Steps to Reproduce

Download the licensee repro here -
Boot in 4.27, PIE, move around the level, the gun with blur quite intensely.

Have Comments or More Details?

There's no existing public thread on this issue, so head over to AnswerHub just mention UE-116769 in the post.

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Affects Versions4.26.24.27
Target Fix4.27
Fix Commit16558641
Main Commit16584879
Release Commit16558641
CreatedMay 27, 2021
ResolvedJun 8, 2021
UpdatedJun 8, 2021
Pull Requests
8104 - erebel55