Commit which added summernote broke the ace editor with a strange change: https://github.com/odoo/odoo/commit/9069d0127c176317436b67b23ae5677dd9d53de7#diff-e9d66a1b466f404be082fa00519eafa5L140. With this change instead of not including the assets bundles in the ace editor and allowing to see them by checking the option, the assets bundles were included when NOT in debug mode and not included when in debug mode.