Hi,
I’m in the same situation overall, although I focus more on strength training.
Physiologically, there is a competition between power/speed on one side and endurance on the other. That’s why 100m runners or elite weightlifters are bad at endurance. And why endurance athletes are bad at speed and power. One study showed that elite marathon runners had a lower vertical jump (yes lower) than healthy sedentary people. These are extreme cases, but this is seen in all athletic clubs, even at the junior level. The one who will be the best in 100m or long jump will be in the last on a 1500m.
These are different metabolic adaptations, but also mechanical adaptations in the muscle fibers.
It’s quite possible that the adaptations in power training can decrease your endurance performance. That being said, I think that in your case, the major reason is that your muscles are still tired after the sessions. And as a result, when you do your skiing, you have less energy. Maybe try to space out your sessions and not do one right before your ski outings.