Pinpoint incoming SMS not received

We are using Pinpoint to receive 2FA text messages and forward them to an email address. This is for a specific use case where testers are not allowed to use their phones for testing an app with 2FA. Pinpoint is configured to publish incoming messages to an SNS topic which is used as a trigger for a lambda function that forwards the message via email.

Mostly, this works just fine. I can send text messages to the phone number, and I can see them being received in the logs. However, when the incoming message contains 'verification code', the message is simply never received by the lambda function. There is no error, the lambda is simply not triggered at all. I tried several variations, but it appears that exact phrase somewhere in the message causes the message to not be received.

Does Pinpoint filter out some messages based on their content? Is there any way of checking that Pinpoint actually receives the message or that it is being blocked prior to reaching Pinpoint?

Thanks.