This CONFIG reliably drops core for me.
############################################ # RUN PARAMETERS ############################################ auto_throttle=1 firstfit=0 bitcnt=7 bloom=1 bloom_bit_count=12 bloom_hash_count=30 bloom_oldest=0 cache=150 checkpoints=1 checksum=on chunk_size=5 compaction=0 compression=none data_extend=0 data_source=lsm delete_pct=44 dictionary=0 evict_max=5 file_type=row-store backups=0 huffman_key=0 huffman_value=0 insert_pct=74 internal_key_truncation=1 internal_page_max=9 isolation=random key_gap=7 key_max=56 key_min=20 leak_memory=0 leaf_page_max=12 logging=1 lsm_worker_threads=3 merge_max=15 mmap=0 ops=100 prefix_compression=1 prefix_compression_min=8 repeat_data_pct=86 reverse=0 rows=100 runs=0 split_pct=66 statistics=0 threads=23 timer=0 value_max=593 value_min=5 wiredtiger_config= write_pct=50 ############################################