The stack hasn't (afaict) changed substantively. I have updated the dependencies: - added cloudinit 1.0.0 - updated runtime from 3.2.0 to 3.2.1 - updated node dependencies from 2.24.1 (and whatever my other packages were at the time I updated to 2.24.1) to 3.2.1 (and all the other latest updates).

Solved. It was caused by the link-to-parent-package.json workaround for lambdas-in-monorepos problem. I had two node_modules directories, supposedly both built from the same package.json, but only one had been updated. Once I deleted the "unimportant" one, everything started working again.