https://icinga.wikimedia.org/cgi-bin/icinga/extinfo.cgi?type=2&host=en.planet.wikimedia.org&service=HTTPS-planet
has been alerting for 13 days.
HTTPS-planet - WARNING 2020-05-04 07:29:29 13d 0h 28m 4s 3/3 SSL WARNING - Certificate *.wikipedia.org valid until 2020-06-20 07:01:41 +0000 (expires in 46 days)
There is also no runbook for that alert on the linked page: https://wikitech.wikimedia.org/wiki/Planet.wikimedia.org
Also CC @RobH as you did certs renewals in the past but not sure who own Planet :)