I had a “Status Checks Change Notice” email this morning from the system, reporting an error.
I tried manually running the Status Checks from the admin page and got the “Error something went wrong” popup. Everything else seemed fine.
I looked at syslog and saw it was checking a domain that I’d let expire some time ago. Unfortunately, I hadn’t deleted the associated mail alias entries for the domain. (My DNS is hosted externally).
It caught me by surprise, because the domain had reached its expiry date some time ago but only now had the registrar removed it from the TLD zone.
Once I’d tidied that up the checks ran normally, and much relief was had!