Assertion Failed in rts/sm/NonMovingMark.c, line 1811

This was raised shortly after startup on our large application running with +RTS -N --nonmoving-gc. This seems to happen maybe one in ten times. I don't have a good repro, but we are running performMajorGC now and then in a thread.

graphql-engine: internal error: ASSERTION FAILED: file rts/sm/NonMovingMark.c, line 1811

Stack trace:
                 0x4a4026f    set_initial_registers (rts/Libdw.c:288.0)
            0x7f4648e848b8    dwfl_thread_getframes (/usr/lib/x86_64-linux-gnu/libdw-0.168.so)
            0x7f4648e84347    (null) (/usr/lib/x86_64-linux-gnu/libdw-0.168.so)
            0x7f4648e84673    dwfl_getthreads (/usr/lib/x86_64-linux-gnu/libdw-0.168.so)
            0x7f4648e84c30    dwfl_getthread_frames (/usr/lib/x86_64-linux-gnu/libdw-0.168.so)
                 0x4a40168    libdwGetBacktrace (rts/Libdw.c:257.0)
                 0x4a2f241    rtsFatalInternalErrorFn (rts/RtsMessages.c:169.0)
                 0x4a2ef2a    barf (rts/RtsMessages.c:49.0)
                 0x4a2ef5c    errorBelch (rts/RtsMessages.c:68.0)
                 0x4a56475    nonmovingIsNowAlive (rts/sm/NonMovingMark.c:1813.0)
                 0x4a5654d    nonmovingTidyWeaks (rts/sm/NonMovingMark.c:1841.0)
                 0x4a5b43d    nonmovingMarkThreadsWeaks (rts/sm/NonMoving.c:924.0)

                 0x4a5b5bf    nonmovingMark_ (rts/sm/NonMoving.c:981.0)

                 0x4a5b484    nonmovingConcurrentMark (rts/sm/NonMoving.c:936.0)

            0x7f464a0694a4    start_thread (/build/glibc-77giwP/glibc-2.24/nptl/pthread_create.c:456.0)

            0x7f4648b9bd0f    __clone (../sysdeps/unix/sysv/linux/x86_64/clone.S:99.0)

    (GHC version 8.10.1 for x86_64_unknown_linux)
    Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

Environment

• GHC version used: 8.10.1

Optional:

• Operating System: debian linux
• System Architecture: x86-64