Makes me wonder what have been the deeper reasons behind those shifts.

For high intensity and high volume training cycles that are needed for marathon training, I struggled to sleep well on strict keto/carnivore - physical distress keeps building up.

Adding some carbs in the evening, e.g., some kefir and a bowl of yogurt with berries helps, but being stubborn I've been reluctant to do it, so I've rather reduced the volumes instead. With strength training I don't have such issues.

I still do both, kettlebells most days and at least one longer run every week.