Hello @cjavier,
Thanks for writing in!
Setting the items to “All” does not mean that it will display all the items. It will actually display the allowable number of items that is a WordPress default. In your case, the max allowed number of items is 10 only. You can increase this by going to Settings > Reading > Blog pages show at most. Just keep in mind that WordPress is using this setting throughout all the archive pages and your blog index. To get your issue resolve, you can change this setting and increase it to 50 or more or you can just edit your layout and set the items to Many with 50 items.

Hope this makes sense.