I just posted basically the same question yesterday, although I've just been dealing with it as-is since I need to continue moving people to a new Windows 10 instant-clone pool as soon as possible. This is causing serious delays. The prospect of having to babysit an app provisioning process over many hours would indicate that something isn't working correctly.
Same issue here. Windows 1803, Appvolumes 2.16 and 2.17, Horizon 7.6 and Horzion 7.5.2.
Someone found a fix or workaround?