Pretty frustrating! Blizzard did say that this would likely be the case, and also pointed out that a beta like this is designed to ferret out bugs, server problems and so forth in time for launch.
While everyone was distracted with Diablo 4's gigantic ... realm" for beta testing upcoming changes, you will occasionally see text pop up while killing monsters in Helltide open world events ...
As I played through my review copy of Diablo 4 a couple weeks ago ... horn that players got for beating the World Boss during the beta. Others, no doubt, will be sold. The horse was one of ...