How much cpu time had the job done at that point in time? 8 hours maybe?

What I think sometimes happens is that a work unit is set to do 6 hours = 100%, but internally checks if 60% of the positions were completed after the initial 6 hours hurdle. If it has, the job goes on to do the remaining positions in the task. Occasionally I observe the percent resetting, but sometimes it does not, so that is what is probably happening. If your job continues to do checkpoints every few minutes you're okay. Just let it run.