While testing a clean JDK9 as of today's date, I ran into the following assert on Solaris/sparcv9 and Solaris/x64:

# Internal Error (/scratch/opt/jprt/T/P1/210316.cplummer/s/hotspot/src/share/vm/classfile/javaClasses.cpp:327), pid=34004, tid=2
# Error: ShouldNotReachHere()

Also in the log file (and printed out just before the assert):

Symbol conversion failure: \u87df\u001a\ufffd\ufffd\ufffd\ufffd\u000c --> \u87df\u001a\u00fe\u0080\u00ff\u00ff