Looks like property setters are called twice as seen https://github.com/openmrs/openmrs-module-webservices.rest/blob/2.37.0/omod-common/src/main/java/org/openmrs/module/webservices/rest/web/ConversionUtil.java#L313-L332, for some resources this leads to a bug where if the setter is for a collection or an array, the collection items are added twice resulting in duplicates when creating a new resource that has a child collection.

I believe this can only be reproduced with 2 levels of nesting of collections e.g. a visit has a collection of encounters and each encounter can have a collection of obs, so if you try to create a new visit with an encounter with some observations.