Thought to Google “intel 660p firmware update” and yes: mine has (had) version 002C, but the most recent version is 005C. Hard to find historic changelogs since Intel sold their SSD business to Solidigm, but one purportedly for 004C copy/pasted to reddit says something about hanging, so let's try it.
Had to jump through a hoop or two to unpack the Solidigm Storage Tool™ (it really wants to be in /usr, not /usr/local, boo), but `sudo sst show --ssd` found the drive and indicated that a firmware update was available, and after taking a slightly-breathtaking minute, `sudo sst load --ssd /dev/nvme0n1` has reported success. What a world we live in. (The last time I was knowingly involved in the process of updating the firmware on a storage device, I wasn't actually the one to do it – Seagate warranty support did, to unbrick my 500 GB drive after the internal uptime counter got too high.) Now it tells me to reboot...