DSW: Training goal and training effect don't match despite high execution score

I use Daily Suggested Workouts based on max HR. For a threshold run, DSW asks me to run at 171bpm (my Zone 5 is 167+, meaning 171bpm = 88% MaxHR counter to this Garmin page that suggests 80-85%). When I do this with a high execution score (95%+), it regularly produces a training effect of "VO2Max" run. When I instead just use my LTHR as determined by Lactate Threshold test in Garmin as a guide (165bpm, 85% of my MaxHR), the training effect ends up as "Threshold" run. I have similar issues with all run types: Base sometimes becomes Tempo, Tempo becomes Threshold.

Because the DSW guidance seems unrealistic / unhealthy, I started to ignore it alongside the execution score. However, this is not ideal because (1) of the negative feedback mechanism (your execution score is terrible!), (2) I have to calculate my own guidance when this is what the watch is for, and (3) I get these alerts about "low heart rate". 

I don't understand why this would happen? Isn't the DSW guidance aligned with the training goal and MaxHR? Can I somehow force DSW to adjust the guidance? 

Thanks for any pointers in advance.