Major - P3 test/format failure, with CONFIG.
The problem appears to be a combination of prepare and truncation, turning either prepare or truncation off in the failing CONFIG makes the problem go away.
[1546546186:659999][10298:0x7fdc127fc700], t, file:wt.wt, WT_CURSOR.next: __wt_cursor_valid, 333: cbt->slot < page->entries ############################################ # RUN PARAMETERS ############################################ abort=0 alter=0 auto_throttle=1 backups=1 bitcnt=3 bloom=1 bloom_bit_count=46 bloom_hash_count=28 bloom_oldest=0 cache=432 cache_minimum=20 checkpoints=on checkpoint_log_size=95 checkpoint_wait=56 checksum=off chunk_size=10 compaction=0 compression=snappy data_extend=0 data_source=file delete_pct=13 dictionary=0 direct_io=0 encryption=none evict_max=0 file_type=row-store firstfit=0 huffman_key=0 huffman_value=0 independent_thread_rng=1 in_memory=0 insert_pct=7 internal_key_truncation=1 internal_page_max=12 isolation=random key_gap=13 key_max=73 key_min=31 leaf_page_max=15 leak_memory=0 logging=0 logging_archive=0 logging_compression=lz4 logging_file_max=67613 logging_prealloc=0 long_running_txn=0 lsm_worker_threads=4 memory_page_max=9 merge_max=19 mmap=1 modify_pct=3 ops=0 prefix_compression=0 prefix_compression_min=2 prepare=1 read_pct=8 rebalance=1 repeat_data_pct=19 reverse=0 rows=1000000 runs=1 salvage=1 split_pct=54 statistics=1 statistics_server=0 threads=24 timer=4 timing_stress_checkpoint=0 timing_stress_lookaside_sweep=0 timing_stress_split_1=0 timing_stress_split_2=0 timing_stress_split_3=0 timing_stress_split_4=0 timing_stress_split_5=0 timing_stress_split_6=0 timing_stress_split_7=0 timing_stress_split_8=0 transaction_timestamps=1 transaction-frequency=46 truncate=1 value_max=983 value_min=4 verify=1 wiredtiger_config= write_pct=69 ############################################