1. Check the Session Logs and troubleshoot the issue. Session log will capture the error. Sometimes, the exception may be from Flow or Apex.

2. Use Omni-Channel routing for Queue-based routing. If you get routableId and/or ContactId null in Flow when passed from the Bot, change the button Routing Type to Omni-Channel to resolve the issue.

In chatbot implementations, Omni-Channel routing is preferred over Live Agent routing. One key difference between Omni-Channel and Live Agent routing is that Omni-Channel creates the LiveChatTranscript record upfront. Live Agent routing creates the transcript record after the chat session is complete. Bot accesses data during the chat session. So, use Omni-Channel based routing.