Odd behavior if more than 10,000 learners?

Summary:

When entering individual completions at the course level, if the course has more than 10,000 learners it in, the system is unable to find the learner even though they were previously added. As mentioned, this seems to occur most often when a course has more than 10,000 learners in it. Each time it is unable to find the learner we have to back out to the find a course screen and start over, and it takes 3-4 minutes each time.

Has anyone else run in to a similar situation? If so, what did you do?

Version (include the version you are using, if applicable):