It appears to be related to starting to use the dependency management plugin to import Reactor's bom. I'm guessing there's a clash between it and whatever was adding the optional dependencies to the pom (the propdeps plugin?).
I'll investigate and hopefully open a PR once I've figured out what the root cause is and how to fix it.
This isn't fixed yet. Since SPR-PUB-4411, we're getting the following:
FAILURE: Build failed with an exception.
* What went wrong:
A problem was found with the configuration of task ':spring-build-src:artifactoryPublish'.
> File '/opt/bamboo-home/xml-data/build-dir/SPR-PUB-JOB1/buildSrc/build/poms/pom-default.xml' specified for property 'mavenDescriptor' does not exist.
Note: "propdeps-maven" is already applied by "gradle/publish-maven.gradle", which is itself applied on all projects but "spring-build-src".