Litespeed backup (Full or T-Log) hangs when CPU throttle parameter is used. The following details may appear in the Job History or error log:
The problem is that the throttling code was relying on throttled threads to terminate before throttling thread was shut down.
When the throttling terminates (or is forcibly terminated) it never iterates through its array of handled "worker" threads and resumes any threads that may be currently suspended. Thus, any threads suspended will hang indefinitely until forcibly killed.
Issue fixed in version 6.0.