Hi @ahmad,
This change is related to our new database system: Significant release of new database schema and additional data
First, to clarify, all the data that was there previously should still be there, and looking up the old mp-id will still return the same material.
To explain further, each material has a set of tasks associated with it, each of these tasks has a unique mp-id assigned. One of this set of task mp-ids is chosen to be the material mp-id. All of the individual task mp-ids should still be presented and still refer to the same tasks, but the specific task mp-id chosen to be the material mp-id may have changed.
For example, Li2WS4 mp-861184 actually has seven distinct tasks associated with it: mp-867695 (structure optimization), mp-862407 and mp-868810 (band structure), mp-861593 and mp-868752 (density of states), mp-861184 and mp-868557 (static calculations). Of these task mp-ids, it looks like mp-867695 was chosen previously to be the material mp-id, but now mp-861184 has been chosen instead. But they both point back to the same material, which is why looking up mp-867695 redirects you to mp-861184.
I’m not sure why specifically mp-861184 was chosen over mp-867695 for this material, maybe @shyamd can comment.
Hope this helps,
Matt