Thanks for your reply.
I am aware of that, but in this case there is only 1 referenced item.
From the docs:
Each returned item can include up to 50 referenced items. If there are more than 50 referenced items, only 50 are returned when the query is run and the partialIncludes property of the returned WixDataQueryResult is true.
If there were more than 50 items, than the first 50 should be returned.
In my case: all the items are returned, but with only 4 fields : _id, _createdDate, updateDate and _owner. All other fields have gone missing.
That doesn’t seem to be expected behaviour of the 50 items-limit?
Also note the UI of the Content manager isn’t showing the referenced Primary Field as well on first load.