ThreadSanitizer: heap-use-after-free lib/dns/resolver.c:1967 in process_sendevent

Job #3348568 failed for 9b57b81e.

WARNING: ThreadSanitizer: heap-use-after-free 
  Read of size 4 at 0x000000000001 by thread T1:
    #0 process_sendevent lib/dns/resolver.c:1967
    #1 resquery_senddone lib/dns/resolver.c:2029
    #2 task_run lib/isc/task.c:859
    #3 isc_task_run lib/isc/task.c:953
    #4 isc__nm_async_task lib/isc/netmgr/netmgr.c:871
    #5 process_netievent lib/isc/netmgr/netmgr.c:943
    #6 process_queue lib/isc/netmgr/netmgr.c:1009
    #7 process_all_queues lib/isc/netmgr/netmgr.c:790
    #8 async_cb lib/isc/netmgr/netmgr.c:819
    #9 uv__async_io /usr/src/libuv-v1.44.1/src/unix/async.c:163
    #10 isc__trampoline_run lib/isc/trampoline.c:213

  Previous write of size 8 at 0x000000000001 by thread T1 (mutexes: write M1):
    #0 free ../../../../src/libsanitizer/tsan/tsan_interceptors_posix.cpp:707
    #1 default_memfree lib/isc/mem.c:744
    #2 mem_put lib/isc/mem.c:656
    #3 isc___mem_put lib/isc/mem.c:1132
    #4 isc__mem_put lib/isc/mem.c:2391
    #5 resquery_destroy lib/dns/resolver.c:1255
    #6 fctx_cancelquery lib/dns/resolver.c:1516
    #7 process_sendevent lib/dns/resolver.c:1962
    #8 resquery_senddone lib/dns/resolver.c:2029
    #9 task_run lib/isc/task.c:859
    #10 isc_task_run lib/isc/task.c:953
    #11 isc__nm_async_task lib/isc/netmgr/netmgr.c:871
    #12 process_netievent lib/isc/netmgr/netmgr.c:943
    #13 process_queue lib/isc/netmgr/netmgr.c:1009
    #14 process_all_queues lib/isc/netmgr/netmgr.c:790
    #15 async_cb lib/isc/netmgr/netmgr.c:819
    #16 uv__async_io /usr/src/libuv-v1.44.1/src/unix/async.c:163
    #17 isc__trampoline_run lib/isc/trampoline.c:213

  Mutex M1 is already destroyed.

  Thread T1 (running) created by main thread at:
    #0 pthread_create ../../../../src/libsanitizer/tsan/tsan_interceptors_posix.cpp:962
    #1 isc_thread_create lib/isc/pthreads/thread.c:81
    #2 isc__netmgr_create lib/isc/netmgr/netmgr.c:355
    #3 isc_managers_create lib/isc/managers.c:28
    #4 create_managers main.c:1065
    #5 setup main.c:1397
    #6 main main.c:1711

SUMMARY: ThreadSanitizer: heap-use-after-free lib/dns/resolver.c:1967 in process_sendevent

Could it be !7868 (merged)? (The only thing merged since yesterday's scheduled run on v9.16.)