I have started experimenting with artifactory up- and download via Jenkins pipeline with artifactory plugin 2.12. Upload was no problem, download failed. Then I saw 2.12.1 and its changes and thought, it would fix my problem. But... A downgrade to 2.11 finally made my small test job work. So there seems to be another bug with 2.12.*. My small pipeline script to reproduce is as follows:

node('unit-tests') {
dir("${MY_WORKSPACE}
CommonTests") {
stage('Download artifacts') {
def downloadSpec = '''{
"files": [
{
"pattern": "repo/BASE-PIPELINE/Binaries/15.80.0/263/sw/",
"target": "sw/"
}
]
}'''

def server = Artifactory.server '***@artifactory.****.net'
server.download(downloadSpec)
}
}
}

Output is:
Started by user
Kuypers,Dirk
[Pipeline] node
Running on slave09.1 in c:\Jenkins-1\workspace\TEST_Artifactory_Download
[Pipeline] {
[Pipeline] dir
Running in D:\WS\CommonTests
[Pipeline] {
[Pipeline] stage
[Pipeline] { (Download artifacts)
[Pipeline] getArtifactoryServer
[Pipeline] artifactoryDownload
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // dir
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
java.io.IOException: Failed to search artifact by the aql 'items.find({"repo": "repo","$or": [{"$and": [
{"path":

,"name":
{"$match":"*"}}]},{"$and": [
{"path":

,"name":
{"$match":"*"}}]}]})': HTTP/1.1 403 Forbidden
at org.jfrog.build.extractor.clientConfiguration.client.ArtifactoryDependenciesClient.readResponse(ArtifactoryDependenciesClient.java:161)
at org.jfrog.build.extractor.clientConfiguration.client.ArtifactoryDependenciesClient.searchArtifactsByAql(ArtifactoryDependenciesClient.java:114)
at org.jfrog.build.extractor.clientConfiguration.util.AqlDependenciesHelper.collectArtifactsToDownload(AqlDependenciesHelper.java:62)
at org.jfrog.build.extractor.clientConfiguration.util.WildcardsDependenciesHelper.retrievePublishedDependencies(WildcardsDependenciesHelper.java:86)
at org.jfrog.build.extractor.clientConfiguration.util.DependenciesDownloaderHelper.downloadDependencies(DependenciesDownloaderHelper.java:83)
at org.jfrog.build.extractor.clientConfiguration.util.spec.SpecsHelper.downloadArtifactsBySpec(SpecsHelper.java:100)
at org.jfrog.hudson.generic.FilesResolverCallable.invoke(FilesResolverCallable.java:47)
at org.jfrog.hudson.generic.FilesResolverCallable.invoke(FilesResolverCallable.java:20)
at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2750)
at hudson.remoting.UserRequest.perform(UserRequest.java:181)
at hudson.remoting.UserRequest.perform(UserRequest.java:52)
at hudson.remoting.Request$2.run(Request.java:336)
at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:68)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at hudson.remoting.Engine$1$1.run(Engine.java:98)
at java.lang.Thread.run(Unknown Source)
at ......remote call to JNLP4-connect connection from 1sp-slave9.rsint.net/10.0.21.186:49496(Native Method)
at hudson.remoting.Channel.attachCallSiteStackTrace(Channel.java:1554)
at hudson.remoting.UserResponse.retrieve(UserRequest.java:281)
at hudson.remoting.Channel.call(Channel.java:839)
at hudson.FilePath.act(FilePath.java:987)
Caused: java.io.IOException: remote file operation failed: D:\WS\CommonTypesTests at hudson.remoting.Channel@786c6371:JNLP4-connect connection from 1sp-slave9.rsint.net/10.0.21.186:49496
at hudson.FilePath.act(FilePath.java:994)
at hudson.FilePath.act(FilePath.java:976)
at org.jfrog.hudson.pipeline.executors.GenericDownloadExecutor.execution(GenericDownloadExecutor.java:41)
at org.jfrog.hudson.pipeline.steps.DownloadStep$Execution.run(DownloadStep.java:66)
at org.jfrog.hudson.pipeline.steps.DownloadStep$Execution.run(DownloadStep.java:46)
at org.jenkinsci.plugins.workflow.steps.AbstractSynchronousNonBlockingStepExecution$1$1.call(AbstractSynchronousNonBlockingStepExecution.java:47)
at hudson.security.ACL.impersonate(ACL.java:260)
at org.jenkinsci.plugins.workflow.steps.AbstractSynchronousNonBlockingStepExecution$1.run(AbstractSynchronousNonBlockingStepExecution.java:44)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:748)
Finished: FAILURE