It seems that the compiler libs reference Js_OO module:

https://github.com/melange-re/melange-compiler-libs/blob/eb8207c1b6744180095184194dfd843e06f9fad1/typing/oprint.ml#L309-L321

After recent changes, those refs are prob broken, they should be either Js__Js_OO or Js.Private.Js_OO.