Issue
When using the "# of responses" option in a Custom Voting rule on a Task step, deployment fails with the error:
Missing reference at ConfiguredVotingCustomRule 'ConfiguredVotingCustomRule' in Event 'Task' in Activity 'Task'. Error: Value cannot be null. Parameter name: count. ..etc
Closing and re-opening the workflow, the "# of responses" box is cleared out.

Error Code

Resolution
- Create the custom voting rule

- Select the radio button for "First response"

- Switch the radio button back to "Custom voting rule"

Deployment should now be possible with the voting rule intact.
Additional Information
This has been logged as a bug and will be fixed in a future version of K2.