First of all, welcome to the forums, @closerlook. Thanks for being a Club member.
Short answer: Set the autoKillThreshold to a lower value (default is 7):
ScrollToPlugin.autoKillThreshold = 3;
And make sure you're using the latest version - the codepen you posted is using a very outdated one. I know, it's counter-intuitive because it's pointing to the "/latest/" directory on the CDN, but unfortunately CDNJS stopped supporting that years ago and they refuse to update files there. We begged...they denied. So just point to /1.20.4/ instead, and you'll be golden.
Explanation: autoKill is enabled by default which means that ScrollToPlugin will automatically check to see if the value that it set on the scroll value last has been changed. If so, that means something else (typically user interaction) made it change, thus the tween should be killed (well, that part of the tween at least). The problem is that some browsers (like iOS safari) are pretty sloppy with those values, so even if (for example) ScrollToPlugin sets it to 112, Safari might alter that slightly (without any user interaction), so we had to build in a tolerance. That's where the autoKillThreshold comes in.
Does that solve things for you?