It might be silly to ask if anyone else is seeing this, as I'm accessing this using a hosts entry on my system. I get SERVFAIL on DNS for both opnsense.org and deciso.com (on my servers), as do some other sites (e.g. mxtoolbox). But not all (e.g. kloth, 9.9.9.9). Offhand, it seems to be an issue with sectigoweb.
In addition... never mind, opnsense.org was renewed - but for one year?
opnsense.org DNS debugging (https://forum.opnsense.org/index.php?topic=52885.0)
Posted 47 seconds later. Heh. (Issue began ~09:00 CDT, some hours ago.) Here for reference.