Can't start river created manualy

There is cluster which consists of two nodes on different machines. I
create custom jdbc river with river's API and I suspect it will start
fetching data from DB right after it's creation. But sometimes it doesn't
start. In 'head' I see _river index with only one document - meta, no
status document created. Why could it happen time to time? What config
parameters could affect this?

Thank you!