Interactive Message Update not replacing original

I have an interactive message with action buttons, but when I reply to the action the original message is not being replaced. Instead, a new message is appearing above the original message:

Untitled

This worked properly before (I don’t know which version MM — we’re currently on 5.23.1), and as far as we can tell nothing changed with our integration that would affect this.

Original message payload:

{
    "channel": "test-channel",
    "attachments": [
        {
            "actions": [
                {
                    "integration": {
                        "context": {},
                        "url": "<REDACTED>"
                    },
                    "name": "I will help"
                },
                {
                    "integration": {
                        "context": {},
                        "url": "<REDACTED>"
                    },
                    "name": "I'm not available"
                }
            ],
            "text": "> This is a test",
            "author_name": "Danny",
            "author_icon": ""
        }
    ],
    "username": "TestBot"
} 

Action response payload:

{
    'update': {
        'message': 'Thanks!'
    }
}

Any idea what could be causing this? I expect it to work like the gif at the end of the Message Button section of the docs.

I have this same issue too. Have you figured out the solution?