(lldb) bt
* thread #2: tid = 0x2ab21, 0x00007fff8b11e01c libsystem_platform.dylib`_platform_memmove$VARIANT$Haswell + 252, stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
    frame #0: 0x00007fff8b11e01c libsystem_platform.dylib`_platform_memmove$VARIANT$Haswell + 252
    frame #1: 0x00007fff939adf1b libsystem_c.dylib`__memcpy_chk + 22
    frame #2: 0x00000001000d21d1 libmongoc-priv.0.dylib`node_not_found(sd=0x0000000100817000, error=0x0000000000000000) + 81 at mongoc-cluster.c:1397
  * frame #3: 0x00000001000cf7e6 libmongoc-priv.0.dylib`mongoc_cluster_fetch_stream_pooled(cluster=0x00000001002888e0, sd=0x0000000100817000, reconnect_ok=false, error=0x0000000000000000) + 310 at mongoc-cluster.c:1644
    frame #4: 0x00000001000cd251 libmongoc-priv.0.dylib`_mongoc_cluster_stream_for_server_description(cluster=0x00000001002888e0, sd=0x0000000100817000, reconnect_ok=false, error=0x0000000000000000) + 161 at mongoc-cluster.c:1444
    frame #5: 0x00000001000cd13d libmongoc-priv.0.dylib`mongoc_cluster_stream_for_server(cluster=0x00000001002888e0, server_id=2, reconnect_ok=false, error=0x0000000000000000) + 413 at mongoc-cluster.c:1509
    frame #6: 0x00000001000c9e44 libmongoc-priv.0.dylib`_mongoc_client_kill_cursor(client=0x00000001002888d0, server_id=2, cursor_id=123, operation_id=551529544, db="test", collection="test") + 308 at mongoc-client.c:1334
    frame #7: 0x00000001000db147 libmongoc-priv.0.dylib`_mongoc_cursor_destroy(cursor=0x0000000100814400) + 471 at mongoc-cursor.c:299
    frame #8: 0x00000001000daf2f libmongoc-priv.0.dylib`mongoc_cursor_destroy(cursor=0x0000000100814400) + 207 at mongoc-cursor.c:275
    frame #9: 0x0000000100004aa6 test-libmongoc`background_mongoc_cursor_destroy(data=0x00000001005d34e0) + 54 at future-functions.c:244
    frame #10: 0x00007fff8dbdbc13 libsystem_pthread.dylib`_pthread_body + 131
    frame #11: 0x00007fff8dbdbb90 libsystem_pthread.dylib`_pthread_start + 168
    frame #12: 0x00007fff8dbd9375 libsystem_pthread.dylib`thread_start + 13
(lldb) f 2
frame #2: 0x00000001000d21d1 libmongoc-priv.0.dylib`node_not_found(sd=0x0000000100817000, error=0x0000000000000000) + 81 at mongoc-cluster.c:1397
   1394	                bson_error_t *error /* OUT */)
   1395	{
   1396	   if (sd->error.code) {
-> 1397	      memcpy (error, &sd->error, sizeof *error);
   1398	   } else {
   1399	      bson_set_error (error,
   1400	                      MONGOC_ERROR_STREAM,
(lldb) p error
(bson_error_t *) $3 = 0x0000000000000000
(lldb) f 6
frame #6: 0x00000001000c9e44 libmongoc-priv.0.dylib`_mongoc_client_kill_cursor(client=0x00000001002888d0, server_id=2, cursor_id=123, operation_id=551529544, db="test", collection="test") + 308 at mongoc-client.c:1334
   1331	   BSON_ASSERT (cursor_id);
   1332
   1333	   /* don't attempt reconnect if server unavailable, and ignore errors */
-> 1334	   server_stream = mongoc_cluster_stream_for_server (&client->cluster,
   1335	                                                     server_id,
   1336	                                                     false /* reconnect_ok */,
   1337	                                                     NULL  /* error */);