I noticed that when I have for example a + in the version the build fails, which is ok I guess. But when I have a + in the version and set a custom image name e.g:

// version that contains a '+'
version="1.6.0-dev.2.uncommitted+wip.foo.c75795d"

and

tasks.named("bootBuildImage") {
    imageName = "registry.example.com/example/example-app:${version}"
}

the build image job runs forever.

See this example app here:
https://github.com/mxab/spring-boot-illegal-version-custom-name-problem