What mechanical issue triggered the abort sequence during the Soyuz MS-10 launch?

Answer

A strap-on booster failed to separate cleanly due to a sensor error

The problem manifested shortly after liftoff when a sensor error reportedly caused one of the rocket's four strap-on boosters to fail to separate cleanly from the core stage, leading to a collision.

What mechanical issue triggered the abort sequence during the Soyuz MS-10 launch?
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