I downloaded the .prox from all notion 6 instruments on my pc. When I insert them it recognize all but those corresponding to the Strings section (violins, violas, celloes, basses). All .prox were installed the same day at the same time. And they're located in the same directory.
It's very rare, because the others were recognized . I think maybe it might be a bug with the latest update, however, I don't know anyone else with this error.