Non reproducable crash, see stackdump below. Most likely depending on configuration of client environment in combination with mongodb server. Please advice.

1005 mongoc-topology-description.c - _mongoc_label_unknown_member_cb d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-topology-description.c(1005)
178 mongoc-set.c - mongoc_set_for_each d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-set.c(178)
1045 mongoc-topology-description.c - _mongoc_topology_description_label_unknown_member d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-topology-description.c(1045)
1519 mongoc-topology-description.c - _mongoc_topology_description_update_rs_without_primary d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-topology-description.c(1519)
1957 mongoc-topology-description.c - mongoc_topology_description_handle_ismaster d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-topology-description.c(1957)
170 mongoc-topology.c -  _mongoc_topology_scanner_cb d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-topology.c(170)
488 mongoc-topology-scanner.c - _async_success d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-topology-scanner.c(488)
132 mongoc-async-cmd.c - mongoc_async_cmd_run d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-async-cmd.c(132)
161 mongoc-async.c - mongoc_async_run d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-async.c(161)
1008 mongoc-topology-scanner.c - mongoc_topology_scanner_work d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-topology-scanner.c(1008)
1292 mongoc-topology.c - _mongoc_topology_run_background d:\projects\mongo-c-driver-1.15.2\src\libmongoc\src\mongoc\mongoc-topology.c(1292)