Hi @resnant, welcome.
Yes, this structure is indeed strange, we have a few “bad” structures on Materials Project. However, the important thing is that these structures are correctly identified as being very high energy. See the “Energy Above Hull” on that page of 2.669 eV / atom – this is exceptionally high. Most synthesizable materials are below around 0.2 eV/atom.
Materials Project is a computational database, we calculate crystals from experimental sources like the ICSD, but also structures that users have submitted or from other projects, some of which are very high energy. These calculations are automated, and we don’t know before calculating them if they will be very unstable or not. Once published, we consider it bad form to “delete” a material even if it is very unstable, since someone may already have referenced it. The important thing is to consult the predicted energies above hull when performing a search.
In future, it’s likely many of these materials will be deprecated, meaning that the data will remain available but they will not show up in search results by default.