So my team also started seeing this issue pop up around the time you posted this. It was intermittent, and we tried tracking it down but could never cause it to happen for our own accounts or test apple accounts we created. Oddly enough, someone from Apple proactively reached out to our team and told us that the Apple URL we are sending people to for them to actually sign into their apple account was using the wrong encoding for spaces. Specifically, the URL had `&scope="name+email"`, and they wanted `&scope="name%20email"`. Once we made the change, we started seeing the `email` claim on every request.
I'm not exactly sure why this would fail intermittently like it did. If it would have failed 100% of the time, it would have been a lot easier for us to figure out.
Not saying this is what is causing your problem, but just wanted to share our experience because we were having the same symptoms!