So about that upside-down lab

Why tf was the Hawkins lab in the Upside-Down melting, and why were their old army guys stuck to the floors and walls? It’s probably a reference to the Philadelphia Experiment, but that happened long before the Upside-Down was created, so it definitely shouldn’t be there, and they went right to the Abyss.

Also, where did the exotic matter even come from? In her panic, El ripped a big whole in the universe, but why did that create a stable wormhole? This isn’t even the first time she’s done that, and the time she sent Henry through didn’t create a stable wormhole. Given that the Upside-Down exists as a wormhole, independent of the portals, why does it persist when the Hawkins portals are closed? What is it connecting the Abyss to in those instances? Also, why is the wormhole fleshy, and seemingly made of the same shit that Vecna’s body is made of? It almost seems like they didn’t think any of this through.

Also, why did the Duffers think that revealing that the Upside-Down was actually just a gateway to a much less interesting dimension that just looks like Nevada during a drought would be a good idea?