Recurring Learning Plan erratic behavior

Summary

Recurring Learning Plan erratic behavior

Content

I'm using a Recurring Learning Plan to manage anti-harassment training that has to be retaken every 2 years.  When I launched it for a group of users, the due date was 12/9/17.  I ran a report on 12/3 and indeed most (not all) of those assigned showed a Learning Plan Progress Due Date of 12/9.  Now I ran the report again today 12/6 and the dates for many people have changed to be 24 months since they last completed the training which in some cases is several weeks later.  What the heck?  Any ideas?

Sally