First, the gate scanners weren't working which caused a clusterfuck at the entrance.
insidethemagic.net
"The backlog of Guests waiting to be scanned at Magic Kingdom began backing up along the Monorail ramps as well as the Ferry docks and bus security checkpoints."
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And then the People Mover erupted a few hours ago...
blogmickey.com
From what I heard from a friend there, the conveyor belt jammed and caused a small fire.

Technical Difficulties Allow Crowd to Enter Magic Kingdom Without Scanning Tickets - Inside the Magic
Large crowds of Guests waited outside Magic Kingdom Park on January 2nd, 2020. Technical difficulties barred MagicBands and Park Tickets from being scanned.
"The backlog of Guests waiting to be scanned at Magic Kingdom began backing up along the Monorail ramps as well as the Ferry docks and bus security checkpoints."
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And then the People Mover erupted a few hours ago...

BREAKING: PeopleMover Evacuated in Magic Kingdom as Smoke Fills the Air
Walt Disney World news, photos, and reviews! We provide you with daily news from the Walt Disney World theme parks and beyond

From what I heard from a friend there, the conveyor belt jammed and caused a small fire.