amplify-backend: Cannot Create Gen2 Projects in my AWS Account at all --> Stack [CDKToolkit] already exists"

Environment information

Environment information is irrelevant - this is happening in the AWS Console

Description

• Scaffold new generic Gen2 project
• Follow docs to add/install gen2
• Get back the right code (Auth and Data) in the repo
• Push repo to github
• Go to AWS Amplify Console
• Start Create new app workflow
• Connect to Git --> correctly detect repo --> correctly pick the right branch
• Steps fail…AWS Amplify Console is just stuck
• Open browser Console, discover the issue

Clicking the “Set Up” button for First time setup required causes the issue:

Here’s what’s in the Network tab of my browser console:

<ErrorResponse xmlns="http://cloudformation.amazonaws.com/doc/2010-05-15/">
  <Error>
    <Type>Sender</Type>
    <Code>AlreadyExistsException</Code>
    <Message>Stack [CDKToolkit] already exists</Message>
  </Error>
  <RequestId>6e2efefd-9751-4a38-81d1-898e3c44a140</RequestId>
</ErrorResponse>

Note: This account was originally created and set up using the AWS Account Bootstrap Kit (which uses CDK). We haven’t touched or updated that in a long, long while. I’m afraid I don’t know what might break if we did, unless there are easy/not-risky steps for that.