Summary:
With Blue Ocean 1.3-beta 1, I am unable to create a Pipeline in a Bitbucket repo which doesn't already contain one.

Steps to recreate:
1. Start with a Bitbucket repo which does not contain a Jenkinsfile. Mine looks like this:

2. Launch Blue Ocean, and create a new Pipeline. Select your Bitbucket server (mine was already set up):

3. Choose the project that contains the empty repo, select the empty repo, click Create Pipeline:

4. As expected, you'll be told that there are no Jenkinsfiles in empty-empty-empty.

5. Click the newly-created "Create Pipeline" button. You'll be taken to the next screen, which is where the failure occurs. You'll get a popup stating "Error loading Pipeline."

6. The only option is to click "Go Back," or you can click outside the boundary of that popup. With either approach, you'll end up back at the beginning of the Pipeline Creation flow:

7. Repeat steps 1 through 4. When you get to the final click of the flow, you'll be told that there's a naming conflict, because empty-empty-empty already exists. You'll have to choose a new name.

8. This loop repeats itself as many times as you want. It is also creating the jobs in Jenkins, but you can only see them from Classic.

9. As a sanity check, I made sure the credentials to my BB server "worked," insofar as I could scan the multibranch pipeline from Classic. This works: