My sincerest apologies for the issue preventing co-op keyboard from working after the Menu redesign, we made a last minute "correction" for localization of the "Enter Room Code" part of the keyboard, well this was actually bad and caused the keyboard to no longer be able to type in the text field.
It should now be corrected allowing you to once again join co-op games.
Thanks for your understanding and being quick to report this bug!
- James