After update our servers to the recent Bitbucket Branch Source Plugin beta and now to the latest release version we have an issue on the "Pipeline: Shared Groovy Libraries" plugin.
We had define some pipeline library (one repo with 3 version/branches) in the Configure Jenkins page. All of them are configured to use Modern SCM of kind git and use an SSH credentials.
Every restart of jenkins instance (for example after update plugins) the pipeline library plugin forgots the SSH credentials field and this cause authentication failure of "git fetch" command in all multibranch jobs.
The problem raised with the beta version of the plugin (now the same in released version).