Hi Katstan,
It sounds like you may be due a recovery day (or more). A smart moved based on yesterday subjective feedback would be to give yourself a rest day, work on sleep and nutrition and attempt your long run on Monday. Please also consider the impact of heat on your training right now.
In regards to the Garmin – the way it is measuring your “training status” is based on how it is collecting training data (Vo2 max, heat acclimation and training load) so if you have been in hot conditions and reduced your training load slightly – Garmin can interpret that as unproductive. here is the definition of unproductive from garmin
“Unproductive: your training load is at a good level, but your fitness is decreasing. Your body may be struggling to recover, so you should pay attention to your overall health including stress, nutrition, and rest.”
So in short I’d say your trip to hotter climate, but nutrition changes are impacting your bodies ability to recover from the training – some rest and a reset with your nutrition and you will be on track in no time.
Leyla