I have noticed that they mostly fail in x86 os running in vm while host is x64, but I've seen x64 fail as well. I just disable Windows Defender. It's too annoying to me.
Thanks for your reply, Murphy78. I experienced it also on real machines x64 cpu x86 and x64 10Pro, Core and Enterprise, but now it suddenly seems to work again. There was a new update "kb3074681" and i tried again and together with that update the defender updates did install this time... I assume it has something to do with ms getting their servers ready for 7-29. Edit: The VM currently running is x86 and the host is x64 and you are wright, that is now the only one who is still not installing the defender update.