There was a @dependabot PR that bumped shelljs from 0.84 -> 0.85: https://github.com/CommE2E/comm/pull/158 that failed for some reason.
Unfortunately the CI logs have long expired, but according to comment left by @ashoat the errors had something to do with flow.
I tried bumping shelljs this time by removing and re-adding the flow-typed dependency from each package.json and it seems to work fine?