This code calls bson_destroy (gle) on the result of a getlasterror call, when the getlasterror call has failed and the "gle" bson object is NULL:

https://github.com/mongodb/mongo-c-driver/blob/a0219c9777f90187fa73d3fa24c66030e0db2a04/src/mongoc/mongoc-write-command.c#L730

The result is a segfault.