MIME type error for deployed online version, not locally

[Lootwig]

Even though running vite dev and also vite preview work locally, after deployment both chrome and safari aren't loading the JS due to this error (this is the chrome version, safari uses different wording):

Failed to load module script: Expected a JavaScript module script but the server responded with a MIME type of "text/plain". Strict MIME type checking is enforced for module scripts per HTML spec.

I'm not sure whether this is due to a change in the adapter or in sveltekit.

This occurs with adapter version 0.9.1 and sveltekit build 504 - I tried downgrading to 0.9.0 and 477, but the behavior is the same (also, undoing all code changes done in the project since using these older versions does not make a difference).