Breaks on latest gatsby, only when there is a webpack cache

It seems like after I start the Gatsby dev server a second time — and webpack has a cache — the worker doesn't load with the exported worker functions set on the object. The moment I clear webpack's cache and restart the dev server, the worker loads fine again.

Does this very limited description by any chance give you a quick insight about what might be causing this?

I'm afraid I can't really give more details, because the inner workings of gatsby/webpack is just one big black box to me.

I can of course make a minimal reproduction with a newly bootstrapped gatsby, if this would be of any help?