Glitchtrap isn't burntrap, nor william's revival, nor a virus at all and you'll say "uh, thats bullshit" but i have my sources.

you know how the animatronics capture the personality of their kids soul when they're stuck on it right?

The Sister Location animatronics were designed to follow up willam's orders

and William was investigating the childs animatronic bullshit back then, he isn't an idiot, of course he would save the AI somewhere

Glitchtrap is that AI, and its orders are to revive william.

Springtrap is still an robot, and he survived one fire so his conscience must've been saved somewhere

i think thats the most reasonable way to explain springtraps third return

because this time it does not make any sense at all, this theory is open to debates.