serverless remove never works because bucket I never created does not exist

Question

I have a lambda s3 trigger and a corresponding s3 bucket in my serverless.yaml which works perfectly when I deploy it via serverless deploy.

However when I want to remove everything with serverless remove I always get the same error: (even without changing anything in the aws console)

  An error occurred: DataImportCustomS31 - Received response status [FAILED] from custom resource. Message returned: The specified bucket does not exist 

Which is strange because I never specified a bucket with that name in my serverless. I assume this somehow comes from the existing: true property of my s3 trigger but I can't fully explain it nor do I know how to fix it.

this is my serverless.yaml:

service: myTestService

provider:
  name: aws
  runtime: nodejs12.x
  region: eu-central-1
  profile: myprofile
  stage: dev
  stackTags:
    owner: itsme

custom:
  testDataImport:
    bucketName: some-test-bucket-zxzcq234

# functions
functions:
  dataImport:
    handler: src/functions/dataImport.handler
    events:
      - s3:
          bucket: ${self:custom.testDataImport.bucketName}
          existing: true
          event: s3:ObjectCreated:*
          rules:
            - suffix: .xlsx
    tags:
      owner: itsme

# Serverless plugins
plugins:
  - serverless-plugin-typescript
  - serverless-offline

# Resources your functions use
resources:
  Resources:
    TestDataBucket:
      Type: AWS::S3::Bucket
      Properties:
        AccessControl: Private
        BucketEncryption:
          ServerSideEncryptionConfiguration:
            - ServerSideEncryptionByDefault:
                SSEAlgorithm: AES256
        BucketName: ${self:custom.testDataImport.bucketName}
        VersioningConfiguration:
          Status: Enabled