What is it?
A dirt resetter.
Yeah basically this. It's set on a timer so everyday at Noon (CST because that's where the server is hosted), all trench bricks in the server are deleted and then reloaded. The Slayer Minigame round ends, and during this resetting period, the Slayer Scoreboard Overlay appears until the resetting is complete, at which time the minigame is reset and gameplay resumes. Designed to be quick and easy, not to disrupt too much.