The environment variables provided by Jenkins itself like e.g. $BUILD_TAG or $BUILD_NO are no evaluated by the plugin and are processed as plain test. For example:

• Assuming that this is the fifth build. / $BUILD_NO is evaluated to 5
• The Maven plugin will evaluated the command "clean install l Maven$BUILD_NUMBER.log" and store the maven log file with the filename "Maven-5.log".
• Archiving the build artefacts with "Maven-$BUILD_NUMBER.log" will archive the file "Maven-5.log".
• Using the text finder to find a pattern in "Maven-$BUILD_NUMBER.log" prints "[Text Finder] File set 'Maven-$BUILD_NUMBER.log' is empty"

Nominal behaviour: Using the text finder to find a pattern in "Maven-%BUILD_NUMBER.log" checks the file Maven-5.log for the specified pattern.