When you specify %t in the log file for garbage collection:
Xloggc:$path/gc%t.log: specifies where the verbose GC data is written to. The %t in the gc log file path will cause the JVM to generate a new file with each JVM restart with a timestamp.
The support-core plugin cannot find the log file used for that, so it doesn't include the file in the bundle. It throws the warning:
The reason is that the code looks for the exact file name, but it should be a pattern: