It seems the displaced mark is already locked.

# Internal Error (hotspot/src/share/vm/runtime/synchronizer.cpp:1254), pid=3475, tid=140084453742336
# assert(dmw->is_neutral()) failed: invariant

Options: -d64 -Xmixed -server -d64 -XX:MaxRAMFraction=8 -XX:+CreateMinidumpOnCrash -XX:+UseG1GC -XX:MaxRAMFraction=8 -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -XX:CompileCommand=compileonly,null::* -XX:-SegmentedCodeCache

ILW = High (assert fails), Low (only seen this once), High (unknown) = P2