iPhone 11 Pro reboots after unlocking it

Try and force restart your iPhone to see if the issue persists

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button.
4. When the Apple logo appears, release the side button.

84% is not too bad, but not great either. The problem could be due to the aging battery, so consider having it replaced and see if that solves the reboots:

iPhone Battery & Power Repair

About genuine iPhone batteries

Repair Provider Verification

(Articles found by searching Apple's Knowledge Base.)

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krystiannoga ~ Does your iPhone 11 Pro still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health & Charging

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