NYC Subway: R211A 4175-4184 test train on the Sea Beach Line at 8th Avenue! (5/1/24)

A Kawasaki R211A consist numbered 4179-4175 + 4180-4184 has recently been spotted performing some sort of testing along the Sea Beach Line's express track on the N. But, both sets had already entered service on the A line. Why is it there? What is it doing? Nobody knows...
This video was filmed on an iPhone 13 Pro Max in 4K at 60fps.
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