puma: Puma silently crashed

Puma silently crashed, there’s no error at all, puma_error.log, puma_access.log as well as production.log are empty. nginx log is also fine before crash. Here is capistrano configuration options:

set :puma_threads, [0, 16]
set :puma_workers, 0
set :puma_worker_timeout, nil
set :puma_init_active_record, true
set :puma_preload_app, true

It can work days before crash, I’ve had 3 crashes for the past two weeks. One was within 20h from start, its brand new server with 64GB RAM, ubuntu 14, we don’t have a lot of users ~ 300 per day, however we have websocket streaming with tubesock.

We also use rollbar for external logging and it’s also empty. We don’t see any spikes on CPU\Memory usage during crashes.

We use Puma 2.8.2, Rails 4.1.4

Is there any way to turn more detailed logging, or find the problem?