High Aerobic Shortage - still no solution

Thank you for your reporting - I have exactly the same issue with my Garmin D2 Mach1 - plenty of low aerobic and anaerobic but ZERO high aerobic - makes no sense to me…

For me it has nothing to do with autodetect on or off. I always had it off because the autodetect gives absolute bogus values (when it was automatically switched on due to a SW update, it set my max heart rate 10 beats/min LOWER than my anaerobic threshold heart rate!).  It's the Garmin labelling of a session (Basic, Tempo, Threshold) which determines if the main part of the exercise load is either added to low or high aerobic. The algorithm used by Garmin is just totally useless.

same issue here started happening since few months while it was okay for years.

high aerobic is not counted at all despite very different kind of rides had.

i'd try but it's very strange as during past 3years i never did a FTP test like suggested and my workouts are so etherogeneous that i'd exepct all three bars to get filled.

i'd also try a new account using same reference values to see what happens..

also today's ride was tagged as "base" 
workout load seems correctly added.

funny fact, a year ago i was struggling with the lack of low aerobic and latter discovered that i was actually training always on high aerobic and anarobic so it was correct..
now i'm stuck to just low aerobic and anaerobic, crazy!

So my simplest solution to get "High aerobic" gain (adding to that orange bar actually) is the following - workout on a smart trrainer including: 15" in HR upper zone 2, then 3 x (6" power at my FTP+5% + 4" HR zone 2), and 10" HR mid-Zone 2. Just this and nothing else. Resulting Training Load will be 100 points, and all those will add up to my "High aerobic" orange bar. Workout is classified as Tempo, however average HR will be just on the top edge of HR Z2 or lower Z3.. Training Effect 2.9-3.0 aerobic. 

Obviously, if I do longer than 6" intervals at power at FTP+5%, or higher power withinn these 6", andór more repetitions than 3, then Training Load will be higher, hence the add-up to "High Aerobic" too. 

Fact is that just a free cycling across all zones & powers, even a tough ride with lots of strain, will NOT add to "High Aerobic" bar, because that is not purely "high aerobic" training session, but a mix of everything which is usually called "unstructured workout". Garmin device seemingly doesn't count such unstructured workouts as "High Aerobic", but dump them all into "Low Aerobic" category, which I would rather call just "Uncategorized". 

And yes, it's extremely challenging to ächieve "Tempo"or "Threshold" workuot classification just riding on the street, if at all possible, I can reach it only by racing all-out for 1 hour WHILE having my average HR in Zone 3 - only then such kind of street ride will get categorised as "Tempo"ot "Threshold" and consequencly the Training Load I earned (usually between 190-210) will add up to "High Aerobic" bar. But these are really hard rides and I need a very known and safe route to be able to push like this for 1 hour. Usually I'm even on gravel tyres @ 2.5 bar to be able to rieach more power at slower speeds.

i can confirm the same but the point is that up to mid-july, at least for me, also unstructured workouts with differend kinds of effors were actually collecting points for High Aerobic load focus, then just not.

totally *** as after each ride, no matter if "productive" "not productive" "peak" "maintaining" has also indication "low high-aerobic load" which is totally no-sense

based on many topics on this forum i can assume garmin has no will to fix this issue or maybe was intentionally modified to act like this thus most of us are forced to stop using garmin virtual coach function

I believe it's NOT a bug (on Garmin's side), but a feature that maybe lacks proper description, so it creates confusion. I was suffering from such confusion too, until I saw that thread (link in one of my posts above( and then I understood. I compared what I learned from Zwift structured workouts, and it all matched together in my mind.

Regarding unstructured workouts that would get labeled by Garin as Tempo, Threshold or VO2max (only such kinds of workouts will result in "High aerobic" gain) - yes it's possible, and as I mentioned above when I'm riding kind of all-out for 1 hour and Avg HR for the ride (I even added this data field to my Garmin screen) falls within HR Zone 4, then such unstructured workout gets classified as Tempo or Threshold, and I get High Aerobic gain approx. +200. In Summer I was able to do this kind of ride 1-2 times per week, and fill in the rest of the week with quite calm HR Zone 2 rides.

this would make sense only if described behavior was always present. instead as I experienced (and not just me) high aerobic points were gained on almost all kind of workouts, not just "tempo, threshold or vo2max".
i also had a mistakenly reported HR threshold value which let most of my workouts to fill JUST high aerobic and had few low aerobic points. latter solved by putting correct HR threshold.

lack of high-aerobic is definitely a bug or a change on algorythm and started to me from mid july 2023. it's totally nosense having 0 points on workouts where you pedal to high aerobic for almost half of the ride just because the remaining workout wasn't at high aerobic.