What does 'nonzero return code 128' in github actions mean?

I'm getting the following error in my github action:

[info] welcome to sbt 1.4.2 (Oracle Corporation Java 1.8.0_222)
[info] loading settings for project workspace-build from plugins.sbt ...
[info] loading project definition from /github/workspace/project
[warn] There may be incompatibilities among your library dependencies; run 'evicted' to see detailed eviction warnings.
[info] loading settings for project root from build.sbt,github_action_sbt_settings.sbt ...
fatal: No names found, cannot describe anything.
fatal: No names found, cannot describe anything.
fatal: No names found, cannot describe anything.
fatal: No names found, cannot describe anything.
java.lang.RuntimeException: Nonzero exit value: 128
    at scala.sys.package$.error(package.scala:30)
    at scala.sys.process.ProcessBuilderImpl$AbstractBuilder.slurp(ProcessBuilderImpl.scala:138)
    at scala.sys.process.ProcessBuilderImpl$AbstractBuilder.$bang$bang(ProcessBuilderImpl.scala:108)
    at co.blocke.gfpack.GFPackagerPlugin$.$anonfun$projectSettings$18(GFPackagerPlugin.scala:60)
    at sbt.internal.util.Init$Value.$anonfun$apply$2(Settings.scala:922)
    at sbt.internal.util.EvaluateSettings.$anonfun$constant$1(INode.scala:211)
    at sbt.internal.util.EvaluateSettings$MixedNode.evaluate0(INode.scala:228)
    at sbt.internal.util.EvaluateSettings$INode.evaluate(INode.scala:170)
    at sbt.internal.util.EvaluateSettings.$anonfun$submitEvaluate$1(INode.scala:87)
    at sbt.internal.util.EvaluateSettings.sbt$internal$util$EvaluateSettings$$run0(INode.scala:99)
    at sbt.internal.util.EvaluateSettings$$anon$3.run(INode.scala:94)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
[error] Nonzero exit value: 128
[error] Use 'last' for the full log.
[warn] Project loading failed: (r)etry, (q)uit, (l)ast, or (i)gnore? (default: r)

At this point my repo has been checked out and JDK 13 has been configured (although I see here it's using Java 1.8 for some reason).

What does 128 code mean?

This builds locally fine. sbt starts locally like this:

[info] welcome to sbt 1.4.2 (Oracle Corporation Java 13.0.1)
[info] loading global plugins from /Users/wmy965/.sbt/1.0/plugins
[info] loading settings for project scalajack-build from plugins.sbt ...
[info] loading project definition from /Users/wmy965/git/ScalaJack/project
[info] loading settings for project root from build.sbt ...
[info] set current project to scalajack (in build file:/Users/wmy965/git/ScalaJack/)
[info] sbt server started at local:///Users/wmy965/.sbt/1.0/server/84b4cffb6c175e13afb2/sock
sbt:scalajack> exit

What is wrong? What "names" is it looking for? (Is there a way to run 'last', like you would on a command line, inside an action in order to see what it's complaining about?)

Here's the workflow yml it's trying to run:

name: Package Release
# This workflow is triggered on pushes to the repository.
on: 
  push: 
    branches:
      - "master"  # only release on a push to main

jobs:
  build:
    name: Release
    runs-on: ubuntu-latest

    steps:
      - name: Set up JDK 13
        uses: actions/setup-java@v1
        with:
          java-version: '13.0.1'
      - name: Checkout repo
        uses: actions/checkout@v2
      - name: Test and Release
        env:
          BINTRAY_USER: ${{ secrets.BINTRAY_UID }}
          BINTRAY_PASS: ${{ secrets.BINTRAY_PWD }}
          BUILD_VERSION: ${{ github.event.ref }}
        id: release
        uses: lokkju/github-action-sbt@master
        with:
          commands: "test; publish"