Some fields are read-only altogether, such as id, created_on, etc.
However, some fields, such as pixel_bundles.tag_type, are available
(or required) on creation, but read-only on subsequent updates.
Add T1.session_id and T1.user_id so that you can observe them.
id,created_on, etc. However, some fields, such aspixel_bundles.tag_type, are available (or required) on creation, but read-only on subsequent updates.