Can't check in and publish documents with Custom Library Definition in the New Experience with SharePoint Online.

Hello.

Since the New Experience rolled out in SharePoint Online I'm having trouble with my Custom Libraries and Publishing Documents.

I can check out documents and generate a minor version (0.2 for example), but I can't publish nor generate a Major Version.

If I turn off the New Experience and get back to the Classic, It works fine.

Any tips?

Thanks in advance.