This is a big release, adding Multi-Library Support. Aa well as the usual advice about backing up your database (there's a non-reversible schema change), it recommends doing a full rescan:

Although this release does not force a full scan on upgrade, you should do it as soon as possible. This is because the multi-library changes affect the move/rename/retag detection and can potentially make you lose annotations (stars, playcounts, playlist references). During the full scan, it will duplicate all your albums, but that's expected. It will remove the duplicates at the end of the scan.