There are several potential problems in this release which are easily fixable
1) site may remain in maintenance mode after upgrade when SMPT Mailer module is enabled, in this case check logs/upgrade.log for any error if everything is ok, then just delete .bx_maintenance file from the root UNA folder
2) if you have Froala editor module installed, then you need to install new FontAwesome Pro module to have toolbar correctly displayed in the editor
3) Froala editor may display message about the license error, then just clear your browser's cache.
Indeed, Una becomes a little gem of technology, another big step towards stability and functionality with this Rc9. So it's worth a big congratulation to Una Team. Many thanks also to consider all our needs, all our ideas and criticisms when they are based on good sen, of course. It's true you've done incredible work and the result is great!