Training status "Unproductive" and VO2max decreasing!

I wouldn't read too much into the training status until your VO2 Max stabilizes. My understanding is that the training status is, at least in part, determined by changes in your VO2 Max.

VO2Max basically compares your HR (as a % of max) to your pace, and works out what kind of fitness level would produce those kind of results. Running in conditions that increase your heart rate (eg. high temperatures, fatigue) will result in a decrease in measured VO2Max.

Training Status compares changes in VO2Max to changes in Training Load, and makes an educated guess as to what is happenning. A decreasing VO2Max as Training Load goes up will result in an "Unproductive" status.

A typical training program might include a block of 3 weeks of progressively increasing training load, followed by a much lighter Recovery week. As fatigue increases along with Training Load, you could well expect to see a decline in VO2Max and a change from Productive to Maintaining to Unproductive over the 3 weeks, followed by Recovery and Peaking as fatigue is eliminated from the system in the final week and your body gets the chance to adapt to the increased demands from the first 3 weeks, resulting in an increased VO2Max.

The results you are describing are pretty much what I would expect going straight from sitting on your butt to busting that butt. :D

Training = Exercise + Recovery. It sounds like you have been working pretty hard, but best results will be achieved by working in some lighter Recovery days/weeks into your overall training program, to allow your body the chance to make the adaptations that are required to actually increase fitness.

What you described pretty much happened to me.
It started in the middle of the good band and the slowly declined. I was expecting better values since I was doing MTB.

It was frustrated but it was spot on, then I joined a training plan and the vo2max started to level off and then raising. After my first lactate test switched to LT zones since they are great for 5k and 10k guidance.