VO2 Up, but training status unproductive

Hi all,

Sorry if this is a duplicate, but I don't see this question for someone only participating in one sport. I only run and have been seeing a decrease in my Vo2 max in the last few weeks. Down 5 points. Not really sure why, similar training load etc, but have had a cold so may be related. However, today my vo2 max increased a little, only 1 point, but my watch says the run was unproductive. I don't see how these two can be true based on the firstbeat explanations that  vo2 Max is linked to status.

Anyone seen this or have any ideas? 

Trying to understand why I'm stuck in an unproductive rut.