The Job Completion Dashboard will backflush any remaining stock material issues for top-level assembly, record remaining production quantities on sub-assemblies, backflushing component material, record remaining production on top-level assembly, mark the job Complete. This is a great-to-have custom process,

However, we have some issues with very large jobs. The processing completes, but the screen gets locked on large Jobs, for example with 500 or so labor records It has improved greatly, but we are going to have to accept a level of trade-off.  

In order to accommodate these large jobs, try using the number of assemblies on each job to help create smaller runs, splitting the posting of Job labor rather than 1 job at a time.  That will slow down the process but accommodate these larger jobs.  Or, just let the process run. Even though the screen locks, the process completes.