I did the suggested sprint workout and got no aerobic points, why?

Sprints are too short to get your heart rate up. That's physiology.

So now the watch hasn't accounted for my Sprint workout and may suggest it again. It should use just the pace and not heart rate when doing sprints to calculate anerobic benefits. 

If the sprints are that short you should just go hard out and forget about chasing numbers. While the sprints might not register in the calculations you can be certain that you are benefiting physiologically. and that benefit will eventually show through in imporv3 VO2max and speed ar VO2max. 

In classifying activities as anaerobic, the watch is primarily looking at the RATE OF INCREASE in HR, not so much the level of HR or the pace.

I'm not sure quite what the effect of starting sprints 5 seconds early is, but it may well be that the outcome is that the rise of HR DURING the interval is not as dramatic. It is also likely that you cant hold the same effort for 20 seconds as you can for 15 seconds. In extending the sprint interval, it is probably LESS anaerobic, not more.

I also agree with Philip that you shouldn't really be looking at pace during sprints - just concentrate on your sprint form and go HARD. If you do want to evaluate pace, perhaps use Last Lap Pace so that you can look at the pace during the subsequent recovery interval.

Looking at your graph of the workout, looks like you did a good job of sticking to the goal.  Sprint hard, recover well.  Heart rate DID go up!  you DID get the low - high - low HR that the workout is looking for.  I often do the same with starting a bit early on intervals, helps in review later or during to have a more accurate 'lap pace' while in the lap with such fast transitions in speed.

Very strange about your Training Load going down?!?!  Sometimes the Garmin Connect data is delayed by a a few hours or even a day... so maybe a wait and see thing to resolve the glitch?   You looked at the Load right before run (not the day before?)?  You are referencing the 7-day Training Load right?   You could have maybe seen a cache'd value from yesterday... then it updated when you looked at it next time?  Or it is as detailed as to the hour... and maybe your hard workout 7 days ago... became 7.1 days ago and got removed from the Load total.  I know for me similar happens occasionally when I do a very high Load long run a week before.... then I do a hard workout, but my I look at graph... "what the heck my Load today is lower then yesterday?!?!  "  --- but then when I look closer I will notice... oh, had a workout with a Load of 230 8 days ago that just got removed!  At least that is how I understand that 7day load data

As far the lack of a high Anaerobic TE... pretty normal , rarely see that get above 2.3, even when doing a super hard short interval session.  

Mine seems to be updating correctly right now - so system at least on my end looks good.

If you don't sprint 5 seconds early the watch records a much slower pace for the rep which messes up the training effect result. It doesn't matter if I can hold that pace or not (Usain Bolt pace for 100 and 200 is the same) I still ran faster than the sprint pace it suggested so it should record as a Sprint.

I didn't look at my watch during the sprint I start 5 seconds early by the beeping countdown and it shows the pace after each rep. 

The algorithm needs work. 

Yeah anything under 300m I start the rep early for more accurate recording. To clarify it was the anerobic pill (4w load) that went down from 242 to 232 (after doing an anerobic workout). I looked at it on my watch post run and on my Connect account before the watch synced to update it so I know it went down. Maybe it would of gone down 10 points anyways yes the Connect reading was day prior so makes sense. It should of gone up but because it recorded the workout as a Base it went down. 

I got a 3.2 anerobic doing 12 x 400 off 1:20 which gave primary benefit anerobic capacity. Is that how many points add to the anaerobic pill 3.2? Its hard to fill that bar the orange and blue bar is always past full. 

just use the 5 seconds warning to start the sprint at the correct pace and you hf is also higher at start

It's just an application. Sometimes errors occur in such applications. However, I perfectly understand your frustration. I know what every minute spent in the gym is worth, and I understand how hard training is. But don't rub too hard; it's just an app. At the beginning of my training, I was also very upset because of such things. The training was very hard. Now I take sarms from https://purerawz.co/; it's like an assistant for building muscle mass. They are much safer than steroids. Now training is much easier for me than before. Just relax.