Deploy preview can't load assets

My deploy previews fail to load some JS assets from Netlify (as a result the site looks completely broken) but as soon as said deploy get published, this issue disappears. Is is expected ? Is there something I am doing wrong. This is a deploy preview:
This is how it looks like once published:
I’d like to point out that this is happening with every single deploy I make: broken when previewed, perfect when published. Am i missing anything ?

@konoufo That does seem odd, but why not fix the issues you already know about before going off in search of new issues? Fixing your previously-existing issues may clear this issue, too.

I can only assume that you have explicit links to your style sheets and images, rather than references. Perhaps consider checking for this!