When editing a CF file and hitting it in the browser (triggering a recompile) on Lucee 5.3.4 and Java 11 update 6, there is no error in the browser, but the web context's application log does fill up with errors related to instrumentation. Note the error message differs based on whether you test with a JRE or a JDK. Lucee 5.3's instrumentation is supposed to be compatible with java 11, but this doesn't seem to be the case. it looks as though the errors are simply being hidden instead.
Note, I didn't test every update of Java 11, but update 5 does seem to have the same behavior, so I assume this affects all Java 11 versions.
Lucee 5.3.4 openjdk 11 u5/u6 JRE - java.io.IOException: Non-numeric value found - int expected
Lucee 5.3.4 openjdk 11 u6 JDK - java.io.IOException: Can not attach to current VM
Here are the CommandBox commands used to start the test servers and the full output in the application log file.