If a job cannot be killed in the operating system, you can force the removal of the job from LSF.
The bkill -r command removes a job from the system without waiting for the job to terminate in the operating system. This sends the same series of signals as bkill without -r, except that the job is removed from the system immediately, the job is marked as EXIT, and job resources that LSF monitors are released as soon as LSF receives the first signal.