We have merged a lot of contacts, because they werde duplicates.
Unfortunately the marketing activities from Customer Insights Journey have not been merged yet.
Answer by Mircosoft to our case:
As discussed, during the merging of two contacts, marketing insights data does not transfer to the active contact. This is the expected behavior of the system.
Unfortunately, there is no workaround available to mitigate this behavior. If you require further assistance, I recommend reaching out to advisory support.
Merging of contacts does not merge marketing insights data
I've had the same problem and same response from Microsoft a few months back.
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