Answer
Rather than trying to hand-construct the internal DATA_TRANSFER-encoded navigation string, use the External Search URL pattern against the Background Jobs OVERVIEW window instead: ifsapf:tbwBackgroundJobs?EXTERNAL_SEARCH=JOB_ID=<job_id>. This doesn't open the specific detail form directly, but it does open a filtered overview list showing just that one job, just one additional click away from its full details — a reliable, simple alternative when the exact DATA_TRANSFER-encoded direct-navigation string can't be reproduced by hand.