Legend won't display on stat

I display uptime stats of multiple systems on a stat widget sourced from Prometheus. At some point (not sure when), the hostname no longer displays. Can anyone offer a suggestion?

Query: sort_desc((node_time_seconds{hostname=~"server|opnsense",job="Linux servers"} - node_boot_time_seconds{hostname=~"server|opnsense",job="Linux servers"}))
Response: {hostname="opnsense", instance="192.168.15.1:9100", job="Linux servers"}

I’m on Grafana 7.2. Thank you.