The issue has been resolved, almost MPC nodes (+9 nodes) are now reachable again.
The MPC network status has been switched back to Optimal on the status page

The MPC decentralized network is currently in a degraded state on the status page.
We are detecting 8 reachable parties, which is below the expected threshold for normal operation.
We are actively investigating connectivity issues and will keep you updated as the situation evolves.