Should I: Create a completely new App ID and submit as a new app?
I do recommend NOT to do so. That would create more confusion, with a risk of being flagged as spam… Or worse, considered as "manipulative or misleading behavior or other fraudulent conduct will lead to your removal from the Apple Developer Program"
Impossible to speak for the reviewer, but some thoughts, hoping it will help.
What type of an app is ? Is it a paying app ? Does it include purchase or subscription ?
Have you checked your app on various simulators (different sizes, iPhone, iPad, Portrait and landscape) ?
Could you go to test flight ? Or at least test your app with a few other people. Their genuine comment may help you understand the issue.
After this, you could either appeal the review or resubmit, explaining what you have done since rejection in the comments to reviewer. Take care to use soft wording, not complaining or criticising the review process in those comments, but just be very factual.