After the Shapella Hardfork, a bug in the code that generates signatures over externally built block headers in Prysm caused invalid signatures to be returned to the mev-boost relays. The relays rejected the signature and no block was published during the slot.
A temporary fix was rolled out to the relays as a stop-gap (there’s no more missed slots happening and no further risk to validators), and Prysm has released v4.0.2 which resolves the signing bug. All Prysm node operaters should update to this release asap, to source blocks from the builder network.
You can find more background, timeline, bug details, patch details and impact in our full write-up at https://notes.ethereum.org/@mikeneuder/ryJGpiBz2 and the post-mortem from Prysm here.
Huge shoutout to Mike Neuder and the ultra-sound team for the collaboration and shared leadership! 
