Commit https://github.com/odoo/odoo/commit/b43364af7258e45ad846fbbf1f375ad26e58eb0d introduced a row in a row. On a standard database, the bug is invisible. When the user wants to edit that event list page, the right column... is not on the right anymore. Note: in 12.0, thanks to BS4, the bug was revealed even more as even on a standard non-edited database, the bug is visible. Closes https://github.com/odoo/odoo/pull/28693