Nexus Repository 3.12.1 was announced 3 days ago. This is an urgent patch release, fixing the bug noted below. You can download 3.12.1 immediately and we strongly recommend it for Maven users using the UI Upload or REST to upload.
UI Upload
NEXUS-17287 - Maven UI/REST API upload results in empty pom
Upgrading from 2.x
If you’re upgrading from Nexus Repository 2, you must first upgrade your installation to 2.14.8. See the upgrade compatibility matrix for more information.