The plugin exports two environment variables named TRIGGERED_BUILD_NUMBER_<jobname>=<buildnumber>. However, if your job has characters outside the alphanumeric range, the variable exported is unusable. Example: my job is named project-builder, then the exported variable will be TRIGGERED_BUILD_NUMBER_project-builder=123. Because of the - character, this variable is unusable. ${TRIGGERED_BUILD_NUMBER_project-builder} does not work.

The copy artifact plugin does a sanitation of the project name in the same export like this for it's COPYARTIFACT_BUILD_NUMBER_jobname environment var:

projectName.toUpperCase().replaceAll("[^A-Z]+", "_")

I think the the regex can be extended with 0-9 as valid characters too actually, but this would be the fix for this problem too.