Dungeons and the System
Shortly after the year 20XX, portals connected to extra-dimensional dungeons appear in the most densely populated areas on Earth. Chaos ensues as dungeon monsters spill out in “dungeon breaks” from the portals, devastating the population.
Luckily, with the appearance of the portals, the “System” arrives as well. The System quantifies humans, monsters, equipment, and objects, and gives out handy magical abilities, allowing humans to fight back.
With the help of the System and their technological prowess, humans exterminate the monsters that invaded the Earth. In order to prevent the monster breaks from happening again, humans must routinely go through the portals to clear out the dungeons. This is because dungeons that are left unattended will slowly spawn monsters inside, until a critical point, upon which the dungeon “breaks” and the monsters flood out onto Earth through the Portal.
What is special about the dungeons are that, following each “clear” of the dungeon by defeating the dungeon boss, and any foreign living beings exit, the System performs a “reset” on the dungeon. Following the reset, the System returns everything in the dungeon to the exact template state.
This reset makes it convenient for waste disposal, as any garbage or toxic waste left inside will be gone upon reset. It also makes it easy for Dungeon Hunters to commit murderous misdeeds, as any bodies and evidence inside the dungeon will disappear upon the reset, and be replaced with the initial state.
The question is, what does the Dungeon/System/Third Party do to the bodies and objects to make them disappear upon a dungeon reset? Are there really no side effects to disposing of foreign objects inside? Are we feeding some Eldritch monstrosity with each Mars bar wrapper, unaware of our impending doom?
The criteria for the best answer is for logical plausibility in relation to the Dungeons and the System, as well as the efficiency of the process. An example of a good answer would have some sort of plausible motive as to why the third party would want to dispose of the bodies in such a way (or a reason as to why the phenomenon happens).