This is intriguing and might be really helpful, thank you!!

In the process of working on this, I discovered that the purge task for the namespace has been erroring, which muddied the waters for me.  I had been assuming that the scads of messages I was seeing in that query were the orphans, but I realize now that is not the case. 

https://wrc.intersystems.com/wrc/eucustprob2.csp?OBJID=996659

I am pretty sure that the bulk of the orphans are this message class:

Class AH.AHLIB.Custom.NextGate.Message.Patient Extends (Ens.Request, %Persistent, %JSON.Adaptor, %XML.Adaptor)

{

Parameter %JSONIGNOREINVALIDFIELD = 1;

Property header As AH.AHLIB.Custom.NextGate.Message.Patient.Header;

Property event As AH.AHLIB.Custom.NextGate.Message.Patient.Event;

Property entity As list Of AH.AHLIB.Custom.NextGate.Message.Patient.Entity;

Property additionalReferences As AH.AHLIB.Custom.NextGate.Message.Patient.AdditonalReferences;

Storage Default

{

<Data name="PatientDefaultData">

<Subscript>"Patient"</Subscript>

<Value name="1">

<Value>header</Value>

</Value>

<Value name="2">

<Value>event</Value>

</Value>

<Value name="3">

<Value>entity</Value>

</Value>

<Value name="4">

<Value>additionalReferences</Value>

</Value>

</Data>

<DefaultData>PatientDefaultData</DefaultData>

<Type>%Storage.Persistent</Type>

}

}

Thank you for the answers! I have a follow up question.

I have been deleting suspended messages already. So how do I go about cleaning up the orphans I've created? 

For instance, in one namespace where I know I deleted some suspended messages (and where all messages older than 7 days are supposed to have been purged), I ran this query:

select * from Ens.MessageHeader nolock
where timecreated < '2025-02-11 00:00:00.000'
order by timecreated 

I get 18298 messages - under four distinct session ids. 

How can I mark these so that will be purged? Or is there some other method of purging these orphans since I deleted their message header? 

Note: These are the settings on our Purge task: