That’s called flashback - it happens when there’s too much power so the laser bounces off the tray and back up into your material.
Solutions include - lowering the power or raising the speed of your cut, masking your material so all the power gets absorbed by the masking, putting down a layer of sacrificial material (this one you have be extra careful because it raises the risk of fire)
Do a search for “flashback” and you’ll find even more advice!
Yup that is flashback. To be that bad your cut is way overpowered. Masking , sanding or cleaning is the choices available. If you want no flashback occuring you are asking that occasionally it does not cut through.