Wow, I’m sorry to be so critical, but after wasting several hours on this I have to say that the handling of “Block Views” in Drupal 8 is wicked-evil bad UI design. While all other blocks show up as you expect them to, block views are nowhere to be found.
Skipping my angst ... if you have created a Block View in Drupal 8, the only way you will find it is by clicking the Place Block button in the Drupal Block Layout interface. Your custom block views don’t show up anywhere else in the Blocks UI, only there.
Actually, it’s a little worse than that. A block view will show up on this page if you (a) add the block view to a region, and then (b) remove it from a region. When you do that, that particular block view will show up at the bottom of this page.