When upgrading to this version from hsd v3.x you must pass --chain-migrate=3 when you run it for the first time.
If you are upgrading from hsd v2.x, then you also need to pass --wallet-migrate=1.
This is a patch release and therefore there are no notable changes. For notable changes in v4.0.0 see those release notes at https://github.com/handshake-org/hsd/blob/4.x/docs/release-notes/release-notes-v4.0.0.md