As I mention in my blog post that reviews this new capability at
https://kaboodlesoftware.com/2025/12/19/the-good-the-bad-and-the-ugly-of-the-new-sharepoint-library-experience/ you can get inconsistencies like this when a library makes use of a SPFx Field Customizer solution. This is because the new library UX does not play nicely with Field Customizers and so to make sure things work as before, the UI reverts to the old UX as soon as it sees a Field Customizer. It's worse that that though because it only reverts to the old UX if the view you are looking at contains the field customizer - if it doesn't you get the new UX.
So, not only do we have inconsistency between libraries we have inconsistency between views in the same library, and worse than that, you are forced to hard-page refresh to get SharePoint to pick up on which UX it should use!
Microsoft really need to fix this as a priority by ensuring that Field Customizers are fully and completely supported in the new UX and not give us a half-backed work around. In fact, what they should really, really have done is given us a switch in library settings allowing us to decide if the library used the new UX or the old one - then most (if not all) of the complaints in this thread would cease to be relevant! It should be a simple fix Microsoft - come on, you can do it for us!
Please continue to give us new features, some of these in the new UX are great but stop assuming that you know better than we do about what we want, especially when what you give us forces us to compromise elsewhere.