For context, I'm using PNPM instead of NPM.
I tried reinstalling all packages with PNPM, now retrying with NPM.

using npm over pnpm did not resolve the issue

It could be different parts of the package, but I don't know much about the internals

Maybe it's the two versions of react-dom , one for the app folder and other for the pages folder

wdym? I'm using the App router, no single reference to the old Pages router

For me when I used the pages folder together with the app folder it appeared two versions but that doesn't seen's to be the your case

any idea what it could be?

It is intentional as one is for the client bundle and one for the server bundle.

Then why are both included on the client.html analysis file?

That happened to me before when I was changing to the app folder