This is a referendum to upgrade Polkadot to v1.2.5. See the Fellowship release notes for more details.
Of special note is the inclusion of the new CheckMetadataHash extension. This is a breaking change for transaction encoding on all chains. Please update wallets and applications accordingly.
Enactment is set for block 21,455,000, which should land on 1 July.
Threshold
Have you performed a RuntimeUpgrade?
Subsquare shows that it will be implemented in 21,455,000 blocks, but the Spec Version is not up yet.