So, I need to somehow re-link the skeleton to the model. Great... I always dreamed of doing modding, I told myself five years ago. Because it's so wonderful, and errors never occur! Sorry, my brain is a bit fried right now. Added after 29 minutes I've fixed absolutely everything. Hooray! Everything works, but now I need to work on new animations. Added after 20 minutes I found another problem - the correct linking of the skeleton. I need to find a balance between rigidity and elasticity, otherwise the animation breaks. But this is not directly related to the topic; I will need to do this either in Blender or somewhere else.