IntelliJ: unable to import SBT project - intellij-idea

Question

I've been using IntelliJ with SBT successfully for a while, but lately I've been unable to import SBT projects.
I'll do the following:
Create new project > Empty project
Specify a new to-be-created folder
Add > Import module in the dialog, or New > Module from existing sources from the menu
Select the folder containing the SBT project
Select SBT
Finish
The project does not show up anywhere in IntelliJ. The status line says "Unable to save settings". If I try to import the project once again I get "This project is already registered".
Here is a snippet from idea.log that looks like it could be relevant:
Caused by: java.lang.Exception: Cannot get libraryTable component state
at com.intellij.configurationStore.ComponentStoreImpl.save(ComponentStoreImpl.kt:166)
... 38 more
Caused by: java.lang.NullPointerException
at org.jetbrains.plugins.scala.project.ScalaLibraryProperties.getState(ScalaLibraryProperties.scala:30)
at org.jetbrains.plugins.scala.project.ScalaLibraryProperties.getState(ScalaLibraryProperties.scala:14)
at com.intellij.openapi.roots.impl.libraries.LibraryImpl.writeExternal(LibraryImpl.java:368)
at com.intellij.openapi.roots.impl.libraries.LibraryTableBase$LibraryModel.writeExternal(LibraryTableBase.java:363)
at com.intellij.openapi.roots.impl.libraries.LibraryTableBase.getState(LibraryTableBase.java:63)
at com.intellij.openapi.roots.impl.libraries.LibraryTableBase.getState(LibraryTableBase.java:45)
at com.intellij.configurationStore.ComponentStoreImpl.commitComponent(ComponentStoreImpl.kt:227)
at com.intellij.configurationStore.ComponentStoreImpl.save(ComponentStoreImpl.kt:159)
IntelliJ 2017.2.3, Scala plugin 2017.2.6.