Monero's get_info returns target_height == 0 when the node is FULLY SYNCED — the field is the height being caught up to, not the chain tip. The '??' fallback left 0 in place, so every healthy node rendered "Syncing — 0.00%, 0 blocks behind" forever. Treat 0/absent as target = own height, the same sentinel electrs_status.rs branches on.