No SMS text message notifications from SmartThings to my Twilio number

My Twilio number will not receive SMS text messages from SmartThings.

I have SmartThings set to send me SMS text message notifications to my Twilio number.

According to the API, SmartThings is sending the SMS text messages:

{
    "destinations": {
        "SMS": {
            "status": "OK",
            "to": "XXXXXXXXXX"
        }
    }
}

https://graph.api.smartthings.com/

According to my Twilio log I am getting no incoming SMS text messages.

https://www.twilio.com/console/sms/logs

This worked a few days ago. Now it doesn't.

SmartThings will successfully send SMS text messages to my mobile phone. And Twilio will successfully receive SMS text messages from my mobile phone.

Is there some rate based blacklist filtering? Do I need to whitelist the SmartThings short code somehow?

Why won't SmartThings send an SMS text message to my Twilio number?

Or, why won't Twilio receive SMS text messages from SmartThings?

It seems Twilio numbers cannot receive messages from short codes.

I found these in Twilio support documents:

Are you expecting to receive SMS from a short code?

Services like Google Voice, Facebook, and Skype, which use short codes (e.g. 55555) to send SMS will not be able to send messages to Twilio phone numbers. This is because short code carriers have arrangements to exchange messages with mobile phone numbers only, and Twilio phone numbers are not considered mobile numbers.

-- Not receiving SMS messages on Twilio phone number

and

Twilio numbers cannot send messages to or receive messages from short codes at this time whether they are Twilio short codes or external short codes.

-- Can my Twilio number send SMS to a non-Twilio short code?

This is disappointing and I do not understand why it worked a few days ago.