Strength training - no calories burnt

I have the same issue. I also don't have anything showing on my training load. I completed a 10k today with a chest strap and have my heart rate and calories showing but nothing on my training load or recovery advisor

As far as I've seen training load should be calculated after 2 trainings/runs. Could you complete a second run and prove that?

My first 945 synced fine as I used TrueUp but this one just isn't logging anything for my training load. I did weights Monday, ran Tuesday, Wednesday and Thursday, then weights Friday, rest Sat and 10k race today... still nothing showing. The only thing it did show was my activity from last week when I used my first 945 (had to return it as the battery was faulty)

I did a hard reset of my watch and just started a strength activity and jumped around for a minute and it showed 1 calorie burned, so looks like this may have resolved it.

I reset my watch twice without success. I just returned it to my seller in order to get another 945.

No problem here. Using my 945 without chest strap, just OHR, and have around 300kcal per hour.

Did you have to change any system settings? Is there any option I'll have to switch on/off? Since this is the second watch showing the same issue(s) I'm afraid it's my fault but I don't know where to look for it...

No, no special system settings. Maybe your OHR is off? I did two specific settings in strength training: Auto-Set detection off and Adjust weight also to off as this is not working as I want and I see no benefit of it. Not sure what the correct english terms are, but should be obvious. You could also try to reset the strength training app to system settings. This should do no harm to the overall watch.

As I understand it, the Strength activity only records calories burned by calculating a static estimation of calories burned based on the amount of *time* spent during a set.

So when you press the button to start the set, calories are estimated based on the number of seconds spent during the set. When you hit the button to stop the set (and start rest time) calories burned goes to zero during rest.

The calorie calculation is completely independent of the amount of weight you're lifting ( bench pressing the bar alone records the same calories as bench pressing 300lbs...) and is based entirely on calculating the aggregate amount of minutes spent during a set multiplied by a basic estimated calorie burn per minute. 

You could sit on a chair, hit the button to start a set and just wait a couple of minutes doing nothing, stop the set and it would record some calories burned.

In my experience the "strength" activity isn't particularly good. Activity detection is weak and I'm not about to go an edit the results after each set -- I'm there to work out, not fiddle with the watch. Someday someone will create a robust wearable for weight training that cleans this up and it would be great. It's an unmet need.