Your code is ok, nothing wrong that would cause it. Especially as it works with other classes. That's probably an issue in the kabook class (template). You could post an issue on GitHub so the author can check and fix it. If you post there, perhaps also add a link to this thread here.
By the way, also I tested it and noticed the same issue. I used the version from Vel's website because that's easy to open in Overleaf, so I'm not sure if the GitHub version is behaving differently.
I've updated the template on LaTeX Templates to v1.3 which corresponds to v0.9.7 on GitHub. The Tex Live 2021 bug is fixed, but I just checked the issue in this thread on GitHub and Federico provided a solution there.
For this template, I would rather not make code changes myself since Federico is actively developing it. The best way to get things fixed is to open an issue on GitHub and he will fix it in the template which will eventually make it over to LaTeX Templates.
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