Missing type id property '_type' (for POJO property 'items') in EHRBase

I start by saying that I already checked the similar “Missing type id property error in Ehrbase” .

My couple template/composition is at this link: Easyupload.io - Upload files for free and transfer big files easily.

The template has been created with the free Archetype Designer. The composition is derived , through the example method, from the template.

The composition can be posted successfully but it cannot be retrieved.

The GET returns the error:
“error”:“Bad Request”,“message”:“DB inconsistency:java.lang.IllegalArgumentException: Could not resolve subtype of [simple type, class com.nedap.archie.rm.datastructures.Item]: missing type id property ‘_type’ (for POJO property ‘items’)\n at …[]… [truncated 9757 chars]; line: 3, column: 8681] (through reference chain: com.nedap.archie.rm.composition.Composition[“content”]->java.util.ArrayList[0]->com.nedap.archie.rm.composition.Observation[“protocol”]->com.nedap.archie.rm.datastructures.ItemTree[“items”]->java.util.ArrayList[0]->com.nedap.archie.rm.datastructures.Cluster[“items”]->java.util.ArrayList[0])”
The error position could be useful if it pointed to the culprit of the problem but just gives a generic problem with items, but which items and what problem ? there are a lot of items in the template.

Any idea of what is going wrong?

Turned out that if I remove all _uid the composition is retrieved correctly as in " Missing fields in uploaded composition"