An issues today (possibly due to a reorg) caused some nodes to stop producing blocks. For most, this was resolved by:
cd MY_NODE_DIR
sudo lukso network stop validator
sudo lukso network stop
sudo lukso network clear
sudo lukso network init
sudo lukso network start
sudo lukso network start validator
Shortly after executing these commands, you should see your “last block” reset to 0 and sync back to the current block. This can take some time. Once synced, your stats and validator processes should reappear in Grafana.