TestFlight review process vs. App Store review process

Solution 1:

Yes, because the TestFlight review is not as thorough or complete.

The assumption (based on what I've seen over a few years as a developer) is that builds in TF are still in development and things can change. It's not a slam-dunk that builds will be accepted into TF because they do some review on them.

For the AppStore, a full review is performed again as if you didn't do TestFlight. I'm guessing they review any notes from the TF team but I don't have proof of that.

So yes, it's possible to be in TF and then fail the AppStore review. It’s also possible for the opposite to happen, you could struggle more in TF review and then breeze through the store process.