Navigation on a child of a MDX+ Category hierarchy does not seem to work

the issue

When I define navigation on a child of a Category member I get the following MDX error when I click on a member:

[Stats].[Top X].[Total].[subtotal].[<child of subtotal category]' is not a known MDX entity

this is the set-up

I have simplified the MDX and transferred it to run on the default Sales cube:

set [level] as [Customers].[Geography].[City]
set [selection] as
filter([level],mid([level].currentmember.name,1,1) = 'A')
+     filter([level],mid([level].currentmember.name,1,1) = 'B')
+     filter([level],mid([level].currentmember.name,1,1) = 'C')

/* MDX + function to create a dynamic hierarchy */    
CATEGORY HIERARCHY [Stats].[ABC], DEFAULT_MEMBER_NAME = "Total",LEVEL_NAME_PATTERN="L - TOP X - ${levelDepth}"
CATEGORY MEMBER [Stats].[ABC].[Total].[subtotal] as [selection] , ADD_CHILDREN=true
CATEGORY MEMBER [Stats].[ABC].[Total].[remainder] as except([level],[selection]),ADD_CHILDREN=false  
 
        
SELECT
{[Measures].[amount]} on 0,
{[Stats].[ABC].[total].[subtotal].children
,[Stats].[ABC].[total].[subtotal]
,[Stats].[ABC].[total].[remainder]
,[Stats].[ABC].[total]}  on 1
FROM [sales]

In the table widget, I have defined the navigation as:

• click behavior: Drilldown
• Drilldown Strategy: mdxExpression
• Drilldown axis: Rows
• MDX Expression:

when $member.name = 'subtotal'  then ic3drilldownStop()
when $member.name = 'total'  then ic3drilldownStop()
when $member.level is [Time].[Calendar].[Month] then ic3drilldownStop()
else nonempty([Time].[Calendar].[Month],[measures].[amount])
end

Result is

Now clicking on, for example, Bogota gives:

Error: [Stats].[Top X].[Total].[subtotal].[Bogotá]' is not a known MDX entity

the question How to solve this error?

The issue is because you're trying to use a category member defined in the SELECT statement itself. As a workaround you could modify your drilldown MDX expression as following:

non empty

case
when $member.name = 'subtotal'  then ic3drilldownStop()
when $member.name = 'total'  then ic3drilldownStop()
when $member.level is [Time].[Calendar].[Month] then ic3drilldownStop()
else nonempty([Time].[Calendar].[Month],[measures].[amount])
end
   
axis 0  ([Measures].[Amount], $member) 

As you can see the expression is not only redefining the axis 1 but the axis 0 as well to mimic the "Filter by" option (i.e., filtering by the Bogota member in your example).