Runner 'The scheduler failed to assign job to the runner, please try again or contact system administrator'

Since upgrading to 15.11 we are experiencing issues where the runner won’t get assigned to the job.

It’s all self hosted, 1 general runner which is availalble and worked previously.

What I see in the exceptions_json.log file which could be a complete red herring is

…exception.class":“NoMethodError”,“exception.message”:"undefined method `pass_user_identities_to_ci_jwt’ for #\u003cUserPreference id: 11, user_id: 14…

This is when trying to re-do a failed job manually.

Anyone got any ideas ?