Order of state updates.

[TomaszSz368]

Unfortunatelly I cannot provide repoducable demo. If I will find issue cause I will try to update it immediately.

Overall issue works like this:
In some cases node is removed from draggable nodes before call of reducer

dnd-kit/packages/core/src/hooks/useDraggable.ts

Line 81 in e9215e8

draggableNodes.delete(id);

This cause that in this line, node is removed from store nodes map before we set activeId:

dnd-kit/packages/core/src/components/DndContext/DndContext.tsx

Line 192 in e9215e8

const activeNode = useCachedNode(draggableNodes, activeId);

And lead to undefined in .get(id):

dnd-kit/packages/core/src/hooks/utilities/useCachedNode.ts

Line 10 in e9215e8

const draggableNode = id != null ? draggableNodes.get(id) : undefined;

I believe this is related to overall performance of application which is used. Standalone @dnd-kit component created by me eg in storybook works fine but inside production application it start to behave like this. That's why I cannot reproduce it.

[TomaszSz368]

Found solution for problem. Instead of removing element on drag from tree I make it opacity 0 so it visually disappear but is not unmounted.