I had trouble with making Bitbucket branch source plugin work, I had a multibranch pipeline created (let's call it mb-1), I was using Jenkins 2.249.1 and I had certificate issues. While trying to solve the problem I upgraded Jenkins to to 2.249.2. When I fixed the issue all worked in existing pipeline

The new issue occured when I tried to create new multibranch pipeline (let's call it mb-2). I configured it EXACTLY as mb-1 (that still works) and the error occurs (esw project exists, works in mb-1, but fails in mb-2):

I checked how it behaves when I use non-existing project as owner:

And the last thing I tried was to create a new multibranch pipeline - mb-3 - as a copy of mb-1, and it works...

So to summarize, on Jenkins 2.249.2:

mb-1 created on 2.249.1 - OK

mb-2 created fresh on 2.249.2, manually configured same as mb-1: NOT OK

mb-3 created fresh on 2.249.2, as a COPY of mb-1: OK