Today in Storm UI I saw this Kafka Spouts Lag:
Id Topic Partition Latest Offset Spout Committed Offset Lag
Kafka Spout test_topic 0 5591087 5562814 28273
Kafka Spout test_topic 1 2803256 2789090 14166
Kafka Spout test_topic 2 2801927 2787767 14160
Kafka Spout test_topic 3 2800627 2800626 1
Kafka Spout test_topic 4 2799391 2785238 14153
Kafka Spout test_topic 5 2798126 2798125 1
Kafka Spout test_topic 6 2796874 2782726 14148
Kafka Spout test_topic 7 2795669 2781528 14141
Kafka Spout test_topic 8 2794419 2780280 14139
Kafka Spout test_topic 9 2793255 2793254 1
Kafka Spout test_topic 10 2792109 2777978 14131
Kafka Spout test_topic 11 2790939 2776817 14122
Kafka Spout test_topic 12 2789783 2775665 14118
Kafka Spout test_topic 13 2788651 2774539 14112
Kafka Spout test_topic 14 2787521 2773412 14109


There was no new messages in that topic for a while, so I expected, that my topology would process all messages. But lag shows me that there's some uncommitted messages in most of topics. Topology stop working and didn't process any messages for few hours.

In logs I found these messages:
2017-02-16 14:50:20.187 o.a.s.k.s.KafkaSpout [DEBUG] Unexpected offset found [2777849]. OffsetEntry{topic-partition=test_topic-10, fetchOffset=2775755, committedOffset=2777978, ackedMsgs=[{topic-partition=test_topic-10, offset=2777849, numFails=0}, {topic-partition=test_topic-10, offset=2777850, numFails=0}, 
........................................
 {topic-partition=test_topic-10, offset=2792107, numFails=0}, {topic-partition=test_topic-10, offset=2792108, numFails=0}]}
2017-02-16 14:50:20.201 o.a.s.k.s.KafkaSpout [DEBUG] No offsets ready to commit. OffsetEntry{topic-partition=test_topic-10, fetchOffset=2775755, committedOffset=2777978, ackedMsgs=[{topic-partition=test_topic-10, offset=2777849, numFails=0}, 
.......................................
{topic-partition=test_topic-10, offset=2792108, numFails=0}]}


So, I assume, messages, that showed as uncommitted, are actually processed by topology and acked. After I start sending new messages to Kafka topic topology start working, but spout lag increasing.
Why spout could stop committing to Kafka?