AWS Lambda and Cognito error on deploy: Only one request to update this UserPool can be processed at a time

Serverless Framework
,
1

In my AWS project, I use the serverless framework to deploy lambda functions and a Cognito user pool.

I want 2 of my lambda functions to be triggered by Cognito user pool events, so here is what I did:

functions:

  auto-move-to-user-group:
    handler: src/auto-move-to-user-group.handler
    name: auto-move-to-user-group
    events:
      - cognitoUserPool:
          pool: test-user-pool
          trigger: PostAuthentication
          existing: True

  auto-validation-user-email-modification:
    handler: src/auto-validation-user-email-modification.handler
    name: auto-validation-user-email-modification
    events:
      - cognitoUserPool:
          pool: test-user-pool
          trigger: CustomMessage
          existing: True

resources:

  Resources:

    MyCognitoUserPool:
      Type: AWS::Cognito::UserPool
      Properties:
        UserPoolName: test-user-pool
        AutoVerifiedAttributes:
          - email
        UsernameAttributes:
          - email
        Schema:
          - Name: email
            Required: True

When I deploy using the serverless deploy command, I sometimes got the following error:

An error occurred: AutoDashvalidationDashuserDashemailDashmodificationCustomCognitoUserPool1 - Failed to create resource.
Only one request to update this UserPool can be processed at a time.

It looks like a random bug, since it doesn’t occurs everytime (happens very often, though). Also, when it occurs, it doesn’t always occurs on the same function.

Did I do something wrong? How can I fix that?

Thanks for your help.