"Before each invasion a signal is sent through the Citadel compelling the keepers to activate the Citadel Relay." -- this is the 9:44 in the video.
This indicates something, like a computer, is telling them to do this.
"after decades of feverish study the scientists found a way to alter this signal."
So they studied this, but where? There on Ilos? And they altered the signal to the keepers, meaning they hacked the computer that sent the signal.
at 10:13 "This time when Sovereign sent the signal to the Citadel, the keepers ignored it."
Wait, what? I thought Vigil just said that the signal was sent through the Citadel compelling the keepers to activate the Citadel Relay. Now Vigil is telling me that the signal is sent from outside the Citadel from a Reaper, Sovereign, compelling the keepers to activate the Citadel Relay. How did the scientists alter the signal from Sovereign?
Who wrote this crap?
And so Sovereign must open the Citadel manually and let the Reapers in because there is no Intelligence on the Citadel to do so. This is in the game. This is in ME1.
Here's the deal. Leviathan was written to fill in the plot ravine about the Intelligence. They created the Intelligence. The Intelligence used their own machine weapons against them in the first harvest to build the first true reaper. The Reapers made the mass relays. The Citadel is a giant mass relay connecting to Dark Space. It also serves to protect the Intelligence from outside attack when it is closed. When it is open everything inside is vulnerable. If the Intelligence had the Citadel Relay built as part of its experiment with the galaxy as Leviathan calls it, it would seem logical that the Intelligence would have itself connected directly to the Citadel Relay, wouldn't it? Of course we're dealing with logic like those who wrote the black text above. "I saw you were building synthetics that were could kill you so I sent a bunch of synthetics to kill you before you built synthetics that would killed you."
And, "That opening the Citadel Relay was bull****, and that 30 ly/day FTL? I gave 'em space magic upgrades and got 'em there in 3 years. I may not control the Citadel, but I control the Reapers. Get some, *****es!"