I don't remember this has happened to me before, but for some unknown reason my last app build does not appear in TestFlight. The archiving and upload went as usual with no problem. And if I try to make a new upload, it says there is already a build with this number (as expected).
Has anyone experienced the same issue and found a working solution?
Check email linked with apple account, you might have received email listing with issues apple found on your build which most of the times related to .plist file for any missing permission description. After removing issues do change the build Number as you cannot upload with the same build number as previous one.