Hi,
I just tried again what Piek2001 suggested - here are my observations:
- I updated to the latest Version of Windows - including the latest Patches.
- I updated iCloud to 7.17 - this version should be equivalent to 10.9.2
- I disabled iCloud Sync by deselecting all the checkmarks.
- I enabled iCloud Sync again
Result:
- iCloud syncs the photo library again - and after this the whole photo library was a mess - many pictures were double, some even triple
- But after the sync the CPU load was low (as expected)
- After this I tried to download the photos of 2020 - everything went fine until suddendly he stopped downloading the photos and the CPU load increased - and stays high all the time. He didn't finish downloading the files of 2020 and he doesn't download new photos anymore - but the CPU is still high.... Process Explorer says "iCloud Photo Library is waiting for an E/A event to finish..."
So finally I decided to de-install iCloud, delete all the directories (with the photos and also the AppData\Local\Apple Inc\... where the info about the photo library is stored).
Then I re-installed iCloud and started photo sync from the scratch. And it worked (maybe because he just syncs new photos and not the existing ones)!
BUT: Then I tried to download the photos of 2020 like before. And again he suddendly stopped downloading the photos and the CPU load increased. At the very same picture/movie than the last time!!!!!! So the behaviour can be reproduced - which for me means that this must be a bug in iCloud for Windows or the iCloud Service!!! From time to time seem to be pictures/movies that cause iCloud for Windows consume so much CPU.
Finally I de-installed and re-installed iCloud once more and now it's working. But I will not try to download the photos of 2020.
Hope that it continues working! I'm wondering for how long...