Loki - Grafana: tooltip contains two instance names, except one

Hi all.
I am not sure why Grafana displays two instance names in the tooltip when using Heatmap, Loki and this query:

sum by (instance) (count_over_time({unit=~"xxxx-player.service|panel-xxxx", service=~"[[service]]"} |= "TV OFF OK" [10m]))

Please advise. I did not find the reason for it or from where it comes…

Thanks a lot.
Radek