"I'm sorry, an internal error has occurred.": Using LLM call to understand user intent and extract correct value to assign to a variable

[tjf-fxp]

What I have done so far:

• I have read all the NeMo-Guardrails docs
• I have updated the package to the latest version before submitting this issue
• I have searched the existing issues of NeMo-Guardrails

Below is the code snippet where i'm trying to assign the month in this format YYYY-MM using LLM call :

$timeframe_flag = ..."Is any specfic timeframe mentioned in $last_user_transcript? If yes, say True, else say False."
      if $timeframe_flag
          $month = ..."Whats the date that your are able to understand from $last_user_transcript? If no year is mentioned then take current year 2025. Give the response in the format YYYY-MM."

This is the response i'm getting from the nemogaurdrails:

System
This is the current conversation between the user and the bot:
User
user action: user said "Any appointments schedule for 21st January?"
Bot
user intent: user ask appointments list
System
Follow these instruction `Whats the date that your are able to understand from var_last_user_transcript? If no year is mentioned then take current year 2025. Give the response in the format YYYY-MM.` to  
generate a value that is assigned to:
$month =
14:14:44.730 | Output Stats None
14:14:44.730 | LLM call took 0.61 seconds
14:14:44.734 | GenerateValueActionFinished | {"action_uid": "13ad...", "action_name": "GenerateValueAction", "status": "success", "is_success": true, "return_value": null, "events": [{"type": "BotIntent",
"intent": "inform internal error occurred"}, {"type": "StartUtteranceBotAction", "script": "I'm sorry, an internal error has occurred."}, {"type": "hide_prev_turn"}]}
14:14:44.745 | StopTimerBotAction | {"action_uid": "7b1f..."}

Note that the return_value is null and the response is: I'm sorry, an internal error has occurred.

But this is the only line of code where LLM call that fails, timeframe_flag is correctly assigned true or false depending on use input:

System
This is the current conversation between the user and the bot:
User
user action: user said "Any appointments schedule for 21st January?"
Bot
user intent: user ask appointments list
System
Follow these instruction `Is any specfic timeframe mentioned in var_last_user_transcript? If yes, say True, else say False.` to generate a value that is assigned to:
$timeframe_flag =
14:14:44.090 | Output Stats None
14:14:44.092 | LLM call took 1.05 seconds
14:14:44.094 | GenerateValueActionFinished | {"action_uid": "00a2...", "action_name": "GenerateValueAction", "status": "success", "is_success": true, "return_value": true, "events": []}
14:14:44.100 | StopTimerBotAction | {"action_uid": "272f..."}

Note the return_value is true this time instead of null.

I appreciate any insights I can get into this to understand why one LLM call fails and the other does not.