Delays in speed and pace makes it impossible to follow suggested sprint workout with Fenix 6X Pro Solar version 12.10 RC

I think that i understand what you mean. Regarding the 10.63 km run with three short sprints. The first sprint reached 158 bpm, the second reached 157 and the third reached 157. But i think that it only was interval 1 and 3 that gave anaerobic points. But im not 100% sure. 

I will probably do a new 10.63 km slow run tomorrow and can try a few short intervals then. One with low starting heart rate and one with higher starting heart rate. Then i can compare the results.

I think the warm up HR affects anaerobic training effect. The warm up HR should be low

I have the same issue on the f6x and speed/distance always from STRYD(wind) +HRM+TRI. 

If I have a target for speed it is easy with stryd to the always the same speed but now with new version soft is harder to have stable speed like you see in my workout speed is too high because it was delays connect.garmin.com/.../5704350513

No, the anaerobic points was 0.0 when the first interval started. I have the data field that shows the points while running. Like this. This picture is from after the first interval. So, first interval gave 0.8 in anaerobic points.

I understand that the Stryd works good but i think that it would be great if Garmin corrected this issue.

Have you try slow run between each interval instead of standing still ? Maybe it will produce higher anaerobic TE

I guess, there isn't any dependency between the few seconds delay and the anaerobic TE. The anaerobic Zone starts at the lactate threshold. This is the point at which the lactate begins to rise exponentially.

So, it's important to know how you've set the LTHR.

If you want a deeper look in the calculation of the anaerobic TE
assets.firstbeat.com/.../FFW609US05-171.pdf

Why did you decide that the human body works the same way? The first 10-15 seconds you run on Phosphocreatine (PCr) . And absolutely no matter 5 and 15 seconds. Sprinting speed depends only on muscle volume and utilization rate (PCr). Based on your age and VO2 max (49)  , sprint training won't help you.

Based on your age and VO2 max (49)

sprint training won't help you.

It's not that clear cut. For the watch to calculate training effect it needs detectable heart rate changes. As already noted this occurs independently of speed/pace; it depends on the fitness level of the individual. Physiologically, there will always be a lag between when a sprint is started and the time taken for the heart rate to reflect the effort. Intervals of around 15s are unlikely to be fully reflected in measured heart rate even from a strap for this reason alone. The sprint finishes as the heart rate begins climbing in response to the effort and then begins lowering before a peak has been reached because the sprint has finished and the rest/recovery has begun. Garmin's estimate of TE is likely based on a full 15s sprint being recorded as a stepped increase from say 140 to 180 then back to 140 when in reality it's a curve that slowly climbs to some value that depends on individual heart rate kinetics before descending again.

The delay in pace has nothing to do with the Training Effect for short sprints where intensity of effort is the important outcome. It's a physiological response of the heart due to exercise. It is important that pace responds quickly but for intervals this short the focus should be on getting to maximum effort as quickly as possible without focussing on pace.

For longer intervals where there is time for pace to settle perhaps intervals greater than 30s, then maintaining a pace within a target range is important and for that reason faster response to changes in pace has greater importance.