Fixed! If you get a chance, feel free to give the game another try. I'm curious to see if my theory was right and Caps Lock was enabled, which caused the game to stop detecting WASD inputs properly.
By the way, after fixing the bugs, I went back and watched the rest of the video. The main inspiration for this game was actually Operius, the official offline browser game for Opera, created by Mors.
That said, I can definitely see how Operius itself might have been influenced by Super Hexagon.
From the very beginning, I knew I wanted to do something with a keyhole. Not just a forbidden door, but specifically a keyhole. The first thing that came to mind was the Digipick lockpicking minigame from Starfield. At some point it just clicked: "What if I combined that with Operius?" And that's basically where the core idea for the game came from.