Cannot update an existing lambda with serverless 1.x

We have several aws stacks that were deployed using Node 4 and serverless 0.5 and now we are trying to move to Node 6 and serverless 1.x. We have migrated the configuration (serverless.yml) and all, but our problem comes when we try to update the actual stack.

Serverless fails at the actual lambda update process with an error like this:

An error occurred: GroupDashshipmentsLambdaFunction - xxx-manifest-service-group-shipments already exists. .

The stack names are the same, and if I change the name of the lambda then it does get created in the right stack.

I know it may be possible to go in and delete the lambdas one by one, but on a production environment this is not really a good thing to do. How can I tell serverless to go ahead and update those lambdas

Any help would be greatly appreciated.