Garmin’s VO2Max (and therefore Training Status) compares HR with your power at that level.
As such, anything that affects HR will affect Training Status as well. Warm weather (or insufficient cooling for indoor workouts), poor sleep, fighting a low level illness, accumulated fatigue, etc can all negatively affect HR and Training Status. Over TRs standard 3 weeks increasing load followed by 1 recovery week pattern, it would not be surprising to see some Unproductive’s as accumulated fatigue builds in week 3. Unproductive is not too much to be concerned about. Overreaching is something that you should take somewhat more seriously.
Occasional Overreaching may be a good thing, but piling on more training stress on top of it may not be the wisest. Personally, I take an Overreaching to be a warning to check my RHR and stress levels more carefully. If they are high and not coming down, I might back off. If they are coming down overnight, I might just continue to train as normal.