One app is not downloading

Apps are not directly transferred between devices. For Apps, the transfer process creates a record of the Apps that are installed on the donor iPad - and it is this record of installed Apps that is transferred to the target device. For Apps that are still available for download from the App Store, the corresponding Apps are automatically downloaded and installed from the App Store.

Not all Apps will, necessarily, continue to be available. Apps may have been removed or retired from the App Store by the respective App Developer. Some Apps may have been abandoned - and may not be compatible with the new device. Where a compatible App is not available, you’ll not be able to transfer/install the App. 

As described, this is very likely the reason that Apps appear to be missing from your iPad. In such cases, there is no workaround.

It’s good to learn that you have successfully worked through - and resolved - the problem.

Old apps from App Store that are a couple of years old may be removed from App Store. If the app is removed, then it is impossible to download to your new iPad.

iOS too low!

Need Updates iPhone or iPad