Conversation agent suddenly starts talking in gibberish

Support Help
1

We are currently facing an issue with the retell voice agent conversation flow where the agent suddenly starts talking in gibberish for no reason. Are you guys aware of this issue and what is the recommended solution to fix this? Please help

Agent ID:

agent_63dabd5bf547ebda9c1ef1f409

Workspace ID

org_zi03os7DAPhVwPYj

2

Hello @sabari.selvaraj

Can you share some Call Ids? Where you faced that issue.

Thank You

3

Sure! Please check this from 5:40

call_4cddf9f61e95a57b7c404f1d8c7

4

Hello @sabari.selvaraj

Thank you for sharing Call ID. I’ve forwarded them to our team for review, and we’ll get back to you as soon as we have an update.

Thank you for your patience!

5

Hello @sabari.selvaraj

It looks like this may have been a transient issue with our voice service during that call. If you’re still experiencing this on more recent calls, please share those call IDs and we’ll be happy to investigate further.

Thank you!

6

I’ve getting the same issue. It is happening on calls with GPT 5.4 nano, claude sonet 4.5, claude opus 4.6. I haven’t tried other models but it seems to be a voice issue rather than an LLM issue.

7

Hello @anthonyg

Please share those recent call IDs where you faced that issues.

Thank You

8

I’m also seeing this issue really often with my agents! Sounds super creepy

Here are the examples just from today, just a few of many…

EX 1: (0:20 sec. mark)
Agent ID: agent_e61005d60481ef4b93dbc8b998
Call ID: call_ab5d835e283d119a7e290690553

EX 2: (3:15 mark)
Agent ID: agent_e61005d60481ef4b93dbc8b998
Call ID: call_96a3ce5acc30c5642b8ab64162b

9

We are still facing the issue where the agent suddenly starts talking in gibberish. Here are the details. We are really annoyed by this issue. Please resolve it soon.

agent_4ba453dd84c59c28e5770a0dc5

call_530a4b9fb6aca7884c54033fcfa

org_zi03os7DAPhVwPYj

10

Hello @sabari.selvaraj

I’ve followed up with our team again and notified them to take another look.

We’ll keep you updated as soon as we have more information.

Best regards

11

Hello @sabari.selvaraj

Have you deleted the agent?

12

Hello Mark1, I believe my team might have done that. Any change you can still diagnose the issue for us? Because, the current system also has this issue

13

Please check this agent and call recording for the gibberish issue. We will ensure this agent is not deleted for now.

agent_13077c7ee7b3c54949934699ee
call_8c496e5414f3dad9066640c025d

14

Hey @sabari.selvaraj

The issue is in your conversation flow’s New_Patient_Collect node. The prompt uses bracket notation [read callingNumber as XXX-XXX-XXXX] as a formatting hint for the AI. When the caller had no caller ID (anonymous), the phone number variable was empty, but the model still attempted to follow the confirmation path and spoke the bracket text literally — which is what produced the gibberish.

Here’s how to fix it:

  • Replace the bracket notation with explicit natural-language instructions, e.g.: “Read the caller’s number back to them one digit at a time in the format XXX-XXX-XXXX.”

  • Add a hard guard for anonymous callers: make the prompt explicitly check if callingNumber is empty before offering to confirm digits, and skip straight to asking for their number manually if so.

  • Optionally, use Retell’s {{variable}} syntax for dynamic values instead of relying on the LLM to interpret bracket directives.

This is a prompt design issue — no platform bug. The TTS, LLM, and telephony layers all worked correctly; the model just output the formatting instruction as spoken text instead of interpreting it.

Thank You