here are the most common options, why you cannot change the content of an attribute, that you might want to check:
1. Check the window in Window Manager if some of the attributes you can't write into are marked as "Read Only" or "Write Once" (doesn't matter the privilleges). If yes it is the best practice to set up an additional window for Admins only (copy one window and set all to "ReadWrite", then set the window selection rules).
2. Check the Object Designer if the attribute you're trying to alter is being calculated or if any calculation is on your attribute. If there is a calculation the value cannot be filled manually but e.g. only via an Action.
Looking at the calculation may give you a hint on how the attribute content is changed.