Course not found error in an existing Learning Plan

Summary

LP created a year ago and utilized; one course resulted in course not found

Content

Has anyone else seen this?  The learning plan has been used for a year and suddenly when the user clicks on one of the courses (& I duplicated it), the result is a screen with the message in the top left, "course not found".  To fix, I deleted the course from the LP, saved, added it back and now it's working.

If it happens again, I'll do better recording of the error but wondering if anyone has seen this anomaly?