If you are using sbt 1.0.2, this problem might be due to a bug in sbt. A fix is expected for sbt 1.0.3.
Related issues:
- https://youtrack.jetbrains.com/issue/SCL-12591
- https://github.com/sbt/sbt/issues/3560
Possible workarounds:
- configure Scala version 2.12.3
- OR downgrade to sbt 0.13.16