Someone in this thread mentions bringing the machine in from the garage to get it out of the cold so I decided to try this. I had to warm the bed with a heat gun because the temp sensor was reading 15°c, so the prints wouldn’t start. With the gun, the temp came up to 17°c, and when the print started it immediately jumped up to something like 55 - 60 °c.
I just switched to octoprint earlier this night, thinking that maybe the issue was related to a USB-on-Mac problem, and thanks to octoprint’s logging, I noticed this peculiarity:
the bed temp spiked low momentarily a couple times