See screenshot:
This happens with other metrics generated by the same exporter.
My only hint is that currently the exporter takes a lot of time to return the data, see:
aborrero@cloudcontrol1007:~ $ curl localhost:12345/metrics -o metrics.prom % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 2980k 0 2980k 0 0 45469 0 --:--:-- 0:01:07 --:--:-- 774k
It took curl 1:07 to complete the query. I wonder if the Prometheus scraper is somehow timing out from time to time.