Summary

As of now (10.6.1), the sorting logic that is used at Advanced Roadmaps for Jira (ARJ) for ordering values treats empty values differently compared to the logic used for JQL issue search navigation view:

1. JQL issue search puts issues with empty values at the bottom of the list
   
2. While ARJ keeps them on top
   

This is expected behaviour since internally ARJ treats empty values as zeros. It is not mentioned explicitly in the documentation for numeric-type custom fields, but the behaviour is the same as for sorting by estimates:

Reference: Sort issues in Advanced Roadmaps

Estimates

Regardless of whether you’re using story points or time estimates (days and hours), the following rules apply:

• Issues without an estimate will be sorted as though they have an estimate of zero.
• Issues that have rolled-up estimate values will be sorted by the total estimate value of a parent issue plus its children.
• If you change the estimation units of your plan, issues will revert to the default sorting order.

Suggested change

While such sorting logic can be suitable for sorting by estimates, it is completely inappropriate for sorting by numeric fields and contradicts user expectations and experience based on the JQL issue search navigation view.

It would make sense to either implement additional logic when sorting is happening based on the numeric custom field on the ARJ plan view. Or introduce additional control that will add sorting possibility without empty values being included/considered.