It looks like some kind of bug. You can file issues here: https://github.com/Scirra/Construct-3-bugs/issues
FYI you're using the Construct 2 runtime in Construct 3 still, which we're going to phase out, so you might want to update to the C3 runtime regardless of this.
Nepeo - looks like in Safari the Opus decoder is returning an ArrayBuffer, then reading a nonexistent .length property of it.