ML classifier returns an empty classification for some threads

See test/data/javacores, any snapshot with state Unknown from the javacore at timestamp 1654508698.407

Also, this 'Running' thread snapshot:

<img width="910" height="389" alt="Image" src="https://github.com/user-attachments/assets/be646c6f-a51f-4ef5-87df-1e940eb28185" />
