"Instrumentation","not found [lucee.runtime.instrumentation.ExternalAgent]

Ubuntu 18.04 LTS
Lucee 5.3.1.102

Logs record this error quite frequently.

What other information can I provide?

"INFO","ajp-nio-8009-exec-4","04/29/2019","14:14:13","Instrumentation","not found [lucee.runtime.instrumentation.ExternalAgent] in ClassLoader [lucee.commons.io.res.util.ResourceClassLoader@ff2fb4d]"
"INFO","ajp-nio-8009-exec-4","04/29/2019","14:14:13","Instrumentation","looking for tools.jar"
"INFO","ajp-nio-8009-exec-4","04/29/2019","14:14:13","Instrumentation","couldn't find tools.jar at: /usr/lib/jvm/java-11-openjdk-amd64/lib/tools.jar"

"tools.jar used: /my/public/directory/web/WEB-INF/lucee-server/context/tools-linux-7u25.jar"

getting the same on Linux version 4.14.104-95.84.amzn2.x86_64 (mockbuild@ip-10-0-1-219) (gcc version 7.3.1 20180303 (Red Hat 7.3.1-5) (GCC))