Security not working correctly, TM1 10.2.2 fixpack 3

[RubenvdLinden]

We have a TM1 application for planning, which uses Cognos security (Cognos BI 10.2.1 fixpack 5).
There are some Cognos BI security groups which were granted permissions to specific nodes in the application. Users in these groups see the correct node(s), however they cannot alter any cell in the planning application. It's completely read-only.

If I "strip" all the rights and group memberships of an existing DataAdmin user (including the DataAdmin rights) and assign this user to one of the security groups, only the correct node is visible and cell alteration is possible as designed.
Why is is not working with new users?