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Excuse me i couldn’t see all the file you sent. In picture number 5 you found white spongy tissue in the wood. So for sure it is a clear symptom of trunk disease.
You should for sure mark the plants with symptoms. You could try to open more the plant trunk and check if this tissue is only in the crown heads or it is extended in the trunk.
If it is only located in the crown head you can try to renew the trunk from it base (over the greff point).
Or you can try to remove all the died tissue with a chainsaw.
Or simply estirpate….