I've tried to import my View, that worked in previous versions, to Alpha 13 and I got the The configuration property display.block_1.display_options.allow.items_per_page doesn't exist. error. I found that the configuration schema for Views block display(block.views.schema.yml) is now a boolean but in reality it is a mapping and that triggered the error.
I'm not sure what goes into the value beside items_per_page so I'm not sure if sequence or mapping is a proper type here. Therefore I'm not creating any patch
Also this bug broke the config import during installation so I'm making it a major priority.