Property right of AssignmentExpression expected node to be of a type ["Expression"] but instead got null

[Redsandro]

I have an Ember project and I'm struggling to ember build -prod this inside a node:8 (docker) container.

Here's ember build -prod on my localhost:

cleaning up... Built project successfully. Stored in "tmp/dist".

Here is ember build -prod in a Docker context:

cleaning up... Build failed. Build Error (broccoli-persistent-filter:Babel > [Babel: app]) in app/node_modules/ajv/lib/ajv.js

app/node_modules/ajv/lib/ajv.js: Property right of AssignmentExpression expected node to be of a type ["Expression"] but instead got null

Not sure what this means, but

 $ npm ls ajv
[email protected] /var/www/app-ember
├─┬ [email protected]
│ └─┬ [email protected]
│   └─┬ [email protected]
│     ├── [email protected] 
│     └─┬ [email protected]
│       └── [email protected]  deduped
└─┬ [email protected]
  └─┬ [email protected]
    └─┬ [email protected]
      └─┬ [email protected]
        └── [email protected] 

Ember is at 3.3, and I've tried multiple fastboot versions from 1.0 beta to 2.x. I was planning to update Ember but need to build a production Docker image before I do the dependency dance. Either way I don't feel comfortable upgrading things before I can get this build to work.

Because why would it work on localhost and fail on the Docker context? I npm ci from the package-lock.json so packages should be identical. Apart from the above mention of ember-cli-fastboot, I haven't got a clue where to begin to research this.