Experiencing the same problem here. Have been rejected multiple times for this issue, despite linking this forum thread.
Updating our deployment target to 13.5 addressed the first round of rejections, and we were approved without any changes to the Apple Sign-in code.
However, we have now received another rejection over a week later for the same issue, again without any changes to the Apple Sign-in code.
As this issue is clearly affecting a significant number of users, it would be greatly appreciated if Apple could offer any sort of direct feedback or advice to address this.