All caches are flushed when a block content entity is created in dxpr_builder_block_content_insert().
There are cases when many blocks need to be created in one http request like cloning or entity actions or content imports.
Clearing all caches is an inefficient way to work around the "front end builder" issue the comment for that hook refers to.
It would be better to either add a cache tag to the render array in question, or invalidate a tag in that hook.
Unknown if this issue is also in 3.x.
Update: There are actually many hooks that have this problem:
dxpr_builder_block_content_delete()
dxpr_builder_block_content_insert()
dxpr_builder_view_add_form_submit()
dxpr_builder_view_delete_form_submit()
Active
2.6
Code