Interesting, I just verified, the hashes do stay consistent through multiple builds as long as the contents don't change.
Might be some other that plugin may be constantly changing something in your build or just a bug in Webpack that probably got fixed in later versions.
Theres hash and contenthash. The latter is computed from chunk content (is deterministic, i hope), so the same input gives same output. Hash is global for the build afair.
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