Stored `ComponentIDKey` and `OperationIDKey` would still use string references (char pointers) to data in related IDs, instead of using the already locally stored std::string name of their matching `ComponentNode` or `OperationNode` for that. During undo, to reduce updates and speedup undo steps, a lot of IDs get 'replaced in place', i.e. new data read from the undo memfile is moved into the existing 'old' ID memory address. And the depsgraph is also re-used from the old BMain. Calling `DEG_id_tag_update` and similar on the ID could then cause depsgraph code to access freed memory from the 'old' data. Joint effort with @sergey and the rest of the depsgraph team, thanks!