This doesn't have any impact in LMS because a user that has already logged in doesn't need to accept policies again until he logs in again, but this blocks WebService calls so it's affecting the app.

Steps to reproduce the problem:

1. As admin, go to "Site administration > User > Privacy and policies > Policy settings" and set "Site policy handler" to tool_policy.
2. Go to "Site administration > User > Privacy and policies > Manage policies" and create a new mandatory policy.
3. In a different browser, login with a user (not admin) and accept the policy. I'll call this user "user A". Do NOT logout with this user.
4. As admin, go to "Manage policies" again and click to Edit the existing policy. 
5. Change anything, make sure the "Minor change" checkbox is unchecked and save changes.
6. With user A, go to your profile > Policies and agreements.
7. In the list of policies, click to Accept the new policy.

At this point, policyagreed is still 0 in the database (user table). The user A is still able to use LMS in the browser, but calling certain WebServices will fail with the sitepolicynotagreed error.

This means the user cannot access the site using the Moodle app because the WebServices fail, but if we check the policies we detect that all of them have been accepted.