Earlier quoted context omitted.
I had Apple point out that I hadn’t yet added a TOS for a trivia app I was making; they’re very thorough.
Almost every rejection has been a matter of "process," like ToS, privacy policy, plist entries, etc. In a couple of cases, they actually found crashes that I missed in my testing.
Trademark use.
I have had apps rejected because I used a trademark (usually Apple's) in my app name or description.
For example, I had submitted an app called "Bluetooth 8-Ball for tvOS".
I was told that "tvOS" was not allowable. I had to use "TV".
This kind of thing has happened a few times. I casually use Apple trademarked terminology a lot, but I can't be as sanguine about it when I submit apps.
Full Disclosure: They also had a problem with the app being a "demonstrator" app. They don't want us releasing apps that they don't think we're "serious" about. They had a point, and I ended up withdrawing the app.