Remove stale/defunct certificate entry from config?

[OpenNonsense]

Hi, I have a certificate entry showing up in the GUI that I cannot delete through the GUI.
"show certificate info" shows nothing. When I try to delete the entry and confirm that I want to delete it, nothing gets deleted. Editing this entry fails with "missing CA key". Downloading doesn't work - nothing happens. (Just did the last two things for testing purposes.)

How can I manually remove this key and config entry from opnsense, please?