Game runs slightly faster after Unity upgrade?

With the recent change from Unity Collaborate to Plastic SCM, I upgraded our Unity engine from 2017.4.31f1 to 2020.3.27F1. I expected there would be some hiccups, which there were, and thankfully most of them were relatively minor. However, there's one that I absolutely cannot figure out. The game now plays slightly faster than before. I wouldn't really care all that much, except that there are portions where the audio is tightly tied to scripted events on-screen, and now they're totally out of sync.

Here's a short video with one such example.

Everything you're seeing here is scripted/on-rails (no input from the player). The underlying code is exactly the same for each. Sprite movement is done by multiplying the same seeds by time.deltatime. Pauses are implemented using waitforseconds in coroutines being fed the same values. And yet, Unity 2020.3 runs faster.

Sure, I could make minor adjustments to my audio or code to make it fit again, but I'd really rather not. It also makes me nervous that perhaps I've done something silly that it's not going to run at a consistent speed across various platforms/machines (though it always has in testing of my previous builds). Is there a simple explanation for this that I'm missing? I'm at a total loss here.

Thanks for any advice you could provide!

EDIT: I should note, I've already confirmed that the game's timescale is still set to 1, as it always has been. I may still be missing something obvious, but it's not that :)