hiya @nebbles and sorry to be slow to get back to you! Have you worked through our build debugging guide yet?
I’d specifically check around making sure that we use the same versions of things to build as you do.
Sounds like you are a thorough individual and so you probably did that already, so I’ll also include my next thought so you don’t wait for another response.
Could you tell us some more about your build pipeline and command? Specifically: do you ever run yarn or npm install yourself, during build? This sounds like some dependencies are being installed by your build, but not cached, and then expected to be present, which might happen if we aren’t the ones installing them - we install somewhat specially, using our own cache dir: