Rasa X 2.X not training after NLU Fallback Implemented

Hello. My team recently deployed a simple Rasa X version 2 for testing that worked. I was then implementing the “Conversation Patterns” from the new docs. At each step I trained and it worked. However, when it came to Fallback and Human Handoff, I got a training error with no apparent debugging after Steps 1 and 2 of Fallback and Human Handoff.

Has anyone encountered this issue or could help? Thank you. @Juste