WHY Obi-Wan's Lightsaber BOUNCED off the Storm Trooper

In Obi-Wan Kenobi show episode 4 in the Inquisitorious HQ, we see him save Leia from the chamber guarded by just 2 storm troopers. As he hacks away, obi-wan's lightsaber BOUNCES off.
Definitely would have preferred obi-wan kenobi's lightsaber to go through, but with little Leia there, I think it makes sense.

Thoughts?

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