This article contains spoilers for Stranger Things season 4.
Stranger Things season 4 ended with the Upside Down invading Hawkins - but the invasion was mysteriously put on hold for two days, allowing the heroes to assemble in their hometown's defense. Stranger Things season 4 introduced a new threat, Vecna, retconned as the Upside Down's greatest threat all along. Born Henry Creel, Vecna had become Dr. Brenner's first test subject, but had been banished to the Upside Down years ago by Eleven.
Vecna sought to bring the Upside Down into a spectacular collision with Hawkins, and he achieved this through a series of apparently supernatural murders. Each one of Vecna's victims was tortured psychologically until he finally killed them, and their deaths tore open small gates into the Upside Down. The Hawkins kids rightly deduced Vecna needed to create four of these gates to bring about this interdimensional collision. Unfortunately he'd already created three gates by the time they figured this out, and they were forced to use Max as bait to draw Vecna out and give them a chance to kill him. They were unable to protect Max, however, and her death opened the fourth gate.SCREENRANT VIDEO OF THE DAY
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But the end of Stranger Things season 4 featured a surprising twist, because the fourth and final gate seemed to seal itself shut - before mysteriously reopening two days later. In narrative terms, this was clearly a plot contrivance to give all the heroes time to get to Hawkins - they'd been scattered across the entire world for the entire season. No in-universe explanation for the delay was provided in Stranger Things season 4, leaving it feeling like something of a plot hole.
Why Stranger Things' Upside Down/Hawkins Plot Hole Is A Problem
The closing scenes of Stranger Things season 4 are the most spectacular in the show's history, and the fifth and final season will build upon them. Until now, the U.S. government has been able to conceal the Upside Down's threat from the town's residents; even the tearing open of the fourth gate was dismissed behind an earthquake cover story. But now the gates are open for good, and ash from the Upside Down is raining upon the town. No doubt it won't be long before Nancy's horrific visions come to pass, with Demogorgons, Demodogs, Demobats, and various other monsters invading. Eleven and her allies are no longer secret protectors; they will inevitably be forced to step out into the open, with all their secrets becoming public knowledge.
The scale of this event makes the two-day time jump feel particularly egregious. It's made worse by the fact it's tied so strongly to the nature of the Upside Down, which is still largely unexplained. According to the Duffer brothers, Stranger Things season 5 is largely set in the Upside Down; "What we haven't really discussed is exactly what the Upside Down is," they admitted. "The big reveals that are coming in Season 5 are really about the Upside Down itself, which we only start to hint at. There is that moment where we realize in episode seven this year that it's frozen in time." It's possible the Upside Down is simply too different a reality to this plane of existence, and the different flow of time meant the dimensions couldn't be aligned too closely. If so, the two-day delay may actually be important setup, pointing to the show's resolution.
But that is far from the only possibility. The fourth gate was opened when Vecna killed Max; but Eleven resurrected Max, which may have resulted in an unstable gate. In that scenario, the fabric of reality initially tore open - but the dimensions began to shift apart again, only coming together once more with the passage of time. It's reasonable to assume Max will awaken from her coma in Stranger Things season 5, and it's possible her consciousness is somehow bound to the fourth gate, giving the Hawkins kids an edge. Alternatively, Vecna may have needed to give things a nudge to open the gates once and for all - and he could have been licking his wounds for the last two days, or else simply waiting until Eleven returned to Hawkins. It may not be a coincidence that the gates reopened shortly after Eleven used her powers to enter Max's mind.
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Ironically, the range of possibility make this Stranger Things season 4 plot hole all the more striking. What's more, most of these explanations frankly feel rather clunky and unsatisfying; they're ways of excusing the plot contrivance, rather than natural and organic parts of the lore. Hopefully the Duffer brothers have a much better explanation in the scripts for Stranger Things season 5.