VO2max not changing during training cycles since the new Edge 1040

same here, also stuck with 59 for months, I am always between 65 and 70, ridiculous. Garmin also does not seem to care about this obvious bug, this thread was locked: https://forums.garmin.com/sports-fitness/cycling/f/edge-1040-series/309188/vo2max-not-updated-on-edge-1040 

I purchased a 1040 a few months ago and the VO2 max is stuck at the same number never changes. worked ok on my 1030+ that I had previously

The question is, was the 65-70 true? :) there is a very simple test to find out how much is your (cycling) vo2max, you need to go all-out for 6mins, that gives you a poweravg (ofc, a very accurate powermeter is needed, a single sided crank or pedal is not a reference powermeter so what is accepted: any Power2Max, InfoCrank, AXS spider, Assioma Duo, or V3/Rally dual, and nothing more) and measure your bodyweight before and after the test (average it) and from this 2 numbers the VO2Max is easily calculated. 

an example: 70kg 6min@ 375w = 65 VO2Max 
                     70kg 6min@ 410w = 70 VO2Max

If you measure your power with a single sided powermeter, and your balance is not 50-50, then your leg balance modify the "power trueness " and modify the Vo2Max estimation too . so with 55-45 % the measured 375W is only 340W , and the 65 Vo2Max is only 59 ( so a powermeter change has also an effect for it. ) and ofc, you need to fill the bodyweight data daily.

The older x30 series has an algorhythm bug , you can fool it with lowHR drift (especially indoor), and very sensitive for the MaxHR setting (lots of user forget to decrease it as the form is getting better and better, the Firstbeat is calculating always from the actualHR/MaxHR ratio to a given power)

The newer x40 series, if you set the "auto MaxHR detection" ON then it always set your MaxHR up and down automatically from its own Firstbeat library data . (so if you start a training block with 190maxHR but after 2-3months it is automatically decreased to 180 by the Garmin unit as an estimation. If you could reach higher maxHR on a workout, ofc it adjust it automatically to this higher value. So this new feature eliminate the old x30 series bug what i mentioned above) If you OFF this auto MAxHR thing, then the Edge wont adjust/modifiy your maxHR in the HR settings, you need to manually modify it. (to get more accurate VO2Max estimation)

I had 79 VO2Max with 830 (went up from 70 in a 3months training block) but I KNEW that it is too much and impossible (i measure the power with Power2Max NG, so my powernumbers are pinpoint accurate..) probably my true is somewhere 68-70 (now in the 840 it is 67 but slightly increasing and almost 68, but it is a very stable value since i bought it last spring or when), my all-time best 6min is 375W (ok, it wasnt exactly on a CP6 test but only a few watts more left in the tank) and i was 66-67kg then. (which is 67-68 VO2Max)

i forgot the most important part of my novel :D

So a summary:

- the x40 has better estimation than the x30 (even with exactly the same input datas, the x30 can heavily overestimate the Vo2Max)

- all estimations are based on input datas, so very important to set accurately : restHR, maxHR, bodyweight and the powermeter must be a dual/total powermeter, those products what i wrote above. If these are good, the estimation will be close to the reality too. I think  in most cases the too low restHR and the too high maxHR in the HRsetting are the culprit.  

Garmin does not use this formula. Garmin estimates the VO2max interpolating power vs HR curve up to HRmax or HR threashold.

Infact you are able to the message about you Performance Condition score immediately at the beginning of your activity when you just pass the HR Z2 limit for some minutes, it starts to record your average power at that HR and it immediately estimates if your Performance Condition is better or worse.

One of the problem with garmin approach, and you can check it. Is that if weather condition changes (above all temperature) VO2max and Performance Condition change. Last year for example I move my training session from the early morning (when generally where I live we have 15°C at 6am in Spring) to the evening (where we have 25°C), and my VO2max decreased from Sunday to Monday, because at the same power with 10 more °C my HR is higher.

we know that Garmin doesnt use that formula, i forgot to write to my comments that with a 6mins all-out effort and with this formula You can calculate your own VO2Max which will be very very close to a lab measurement (we can say: equal). So if this formula gives you a lower (or in rare cases, higher ) VO2Max than the Garmin's own estimation, then some settings are wrong in the Garmin. (because what the Garmin gives you that is fake, lots of people like to show their obviously fake VO2Max screen on Strava , i'm just laughing on them... :)
You cant fool so easily the x40 as you can the x30, i tried...  :) 

I'm using a 1040 for most rides, sometimes use my fenix 6 for trainer sessions. I've found there is alot of inconsistencies recently, esp with VO2Max.   Recently,  the graph on both devices stopped giving that line and the calculation seems to have stalled.

My FTP has improved and my weight has dropped - to me that would indicate that the number should shift, right?
Also my acute load is high, and my load focus is high Aerobic (and within optimal ranges for the other two sections), HRV is within normal range, but I'm in recovery training status? 

Question to all, are you using the 1040 as the primary training device or your watch?

My settings:

• Edge as Primary Training Device (PTD)
• Fenix as Primary Wearable Device (PWD)