>>531116570
The school events are poorly programmed.
Every teacher has a fully voiced morning class introduction event where they present themselves and talk about what they'll teach Nagisa's class, and then the rest of their events are unvoiced.
What's weird is that you might see this fully voiced event long after you've already had that same teacher give a lecture and ask you a question prior.
That happened to me with picrel and the literature teacher.
Don't think too hard about it. There's little to no quality control in a lot of the game's aspects.