This happens intermittently with:

$ CONF=linux-x86_64-server-fastdebug make images run-test TEST=gc/stress/CriticalNativeStress.java TEST_VM_OPTS="-XX:+UseShenandoahGC"

#
# Internal Error (/home/shade/trunks/jdk-jdk/src/hotspot/share/gc/shenandoah/shenandoahNMethod.cpp:211), pid=58755, tid=58785
# assert(_nm->is_alive()) failed: only alive nmethods here
#
# JRE version: OpenJDK Runtime Environment (16.0) (fastdebug build 16-internal+0-adhoc.shade.jdk-jdk)
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 16-internal+0-adhoc.shade.jdk-jdk, compiled mode, sharing, tiered, compressed oops, shenandoah gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x14ee9a4] ShenandoahNMethod::assert_alive_and_correct()+0x424
#

Current thread (0x00007f4350003180): GCTaskThread "Shenandoah GC Threads#16" [stack: 0x00007f43541bb000,0x00007f43542bb000] [id=58785]

Stack: [0x00007f43541bb000,0x00007f43542bb000], sp=0x00007f43542b9b60, free space=1018k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x14ee9a4] ShenandoahNMethod::assert_alive_and_correct()+0x424
V [libjvm.so+0x14f00b7] ShenandoahNMethodTableSnapshot::parallel_blobs_do(CodeBlobClosure*)+0x87
V [libjvm.so+0x1478683] ShenandoahConcurrentRootScanner<true>::oops_do(OopClosure*, unsigned int)+0x553
V [libjvm.so+0x146fcba] ShenandoahMarkConcurrentRootsTask::work(unsigned int)+0xda
V [libjvm.so+0x17b5920] GangWorker::loop()+0xe0
V [libjvm.so+0x1680926] Thread::call_run()+0xf6
V [libjvm.so+0x12aa27e] thread_native_entry(Thread*)+0x10e