Eventing Service: Backlog not getting processed

I created the sample enrich_ip_nums function on a beer-sample bucket using 5.5 Beta,

after running pillow fight against the bucket, there were 29.4K eventing failures.

I've no idea what is failing here, the logs are at TRACE level.   The backlog is 430k and not getting processed. 

I did run pillowfight with TTLs.   Possibly this line might be of interest.

2018-04-18T11:30:56.505+00:00 [Info] eventing-consumer [worker_enrich_ip_nums_2:/tmp/127.0.0.1:8091_worker_enrich_ip_nums_2.sock:6956] Bucket: LCB_GET callback, res: The key does not exist on the server13 cas 0

Should this be logged as Info or Error ?

If it is caused by expired docs, how do I clear the backlog ?