Thanks for posting your log @glantucan. Indeed you are receiving the same error as @utdev.
Error: readdirp: root argument is required. Usage: readdirp(root, options)
This is also the same error received by @robhicks (see: Node version not being set using .nvmrc in root of monorepo or as NODE_VERSION envar) though using SvelteKit not Next.js. @hrishikesh has posted some potential solutions you might like to try (though not sure it is entirely solved yet.)
The common element through all three is
readdirp (/opt/buildhome/.netlify-build-nvm/versions/node/v12.16.3/lib/node_modules/@netlify/build/node_modules/readdirp/index.js:262:11)
Hopefully a Support Engineer will have more information on this issue soon. Hang tight.