I created a new account to comment here; and found that Ross explained the exact same experience that I wanted to add. Recently I faced a situation where an app update was rejected for an issue that didn't even exist in that build. Tried pushing another build, tried appealing, no use, the response was the same. Later I realized that there was an old APK file in the "Open Beta" channel which was uploaded 2 years ago, which had the mentioned problem. The beta channel was still open, but nobody knew that. I deleted the Open Beta and then resubmitted, it got accepted. The problem is, they never mentioned anything about which specific APK in which track has this problem. Just like Ross said, they must be combing all the latest APKs published in all active channels.