My guess is that you are populating the "Can Read" field on Articles but are trying to put a "Users who can access all Articles" as a "Can Read" on the Knowledge base to override that Article level "Can Read"?
Unfortunately in this case, that is the opposite order that it filters.
It will first determine if a user can read the Knowledge base and then further evaluate if the user can read the Article itself. If the user does not pass the Article's "Can Read", then the user will not be able to see the Article even if they pass the Knowledge Base's "Can Read".
Contributors get access to read all Articles in the Knowledge Base (assuming they do not hit a "Cannot" condition and/or functionality your Company may not use like "Ownership Group") because they must maintain the Articles in the Knowledge Base so they need to be able to see all Articles so that they can update them when needed.
More info can be found in the "Flowchart showing how read access to a knowledge article using user criteria is evaluated." section of the "Managing access to knowledge bases and knowledge articles" ServiceNow Docs.
