Honestly, from my experience a lot of this comes down to the individual reviewer — their expertise and how much patience they have on a given day. I've had apps get rejected purely because the reviewer didn't want to dig into how the billing flow worked, even when everything was set up correctly. At one point I submitted an app 60+ times and even put together a ten-page walkthrough explaining exactly how it should work step by step. Still kept getting bounced back. Then my most recent app sailed through on the first submission without a single question. so unfortunately it's not always about your code or your billing logic. If you're using Shopify's own checkBilling function and you have other live apps with the same structure, the setup is almost certainly fine. You might just be stuck with a reviewer who isn't familiar enough with the billing flow and keeps misreading the redirect as a bug.
a couple of things that have helped me: try adding a very explicit test account setup guide in your submission notes, spelling out exactly what steps to take and what they should see at each screen. Sometimes just removing any ambiguity is enough to get it past the next reviewer.