How to attach a JS library to page or block with #attached?
This might be a simple case of misunderstanding. The difference between libraries_load and library #attached keys can be confusing. 

['#attached']['libraries_load'] is for libraries defined through hook_libraries_info which is in turn a part of the Libraries API module. If a module has defined a hook hook_libraries_info but your installation doesn't have the Libraries API module installed, then that library will never load. The libraries_load key of #attached will not fire for the same reason. Ideally though, this module with the hook_libraries_info should have a dependency on the Libraries API module if it was written correctly.

['#attached']['library'] is for libraries defined through drupal core library api hook_library. This should always work without any additional modules, provided you've defined a hook_library in your module (and not hook_libraries_info)

Hope this helps you get a clearer idea of what's exactly wrong. You can't have these interchanging, and just trying libraries_load or library randomly to see if they work. Both require a certain prerequisite (see above) to function correctly.