Version conflict (409) question

Is version conflict bulk write error (409) only occur when I'm updating the same document from 2 different writers?
I am starting to see this error more often in our system and trying to figure out if our data pattern has changed or it's something else.
The other possibility is ES7.15 raised this to error level comparing to ES6 so I'm seeing it more now?

That's a likely cause, yes.

thanks.