mk2s: no calories and training effect for freedive and spearfishing

My descent mk2s says that after long sessions of freediving or spearfishing I burnt zero calories and the activity doesn't impact my training status. I tried to use also hrm pro to register the heartbeat under the wetsuit. The heart data appear in the garmin dive app but this doesn't affect calories and training status.

I use the watch to do many activities (running, mountain biking, etc.) and I'm very happy with the possibility of tracking my status (training status, burnt calories, etc.) across all these activities but this doesn't work when I do freediving and spearfishing. That's very bad. For instance, yesterday I did a 4 hours session of spearfishing, which is a very intense activity, but today the watch tells me that I'm going to be unproductive and I'm resting too much, because yesterday's activity means nothing for the algorithm.

How can I solve this issue? I cannot believe that this is a bug of every descent mk2, it would be an incredible oversight on the part of those who designed it.