Hi,
I tried but could not reproduce your problem with fresh project using CUBA 7.1.5 and PostgreSQL. Jdbc driver is re-packed and included into the app.jar along with other libraries.
If the problem persists, I would advise to check contents of your build.gradle file, compare it with contents of the file being created by Studio for new projects.
OK, thanks. I thought I did that, but clearly I missed something. Is there any way to see the buildUberJar source code or debug it? Maybe turn on some kind of detailed logging of the process?