Pixelmator Photo and iCloud Drive: corrupted photos

I have some photos on iCloud Drive (note: not iOS Photos/iCloud Photos), added from a Windows PC. I want to make some edits using Pixelmator Photo on an iPad Pro (2020; iOS 13.5). I open the photo - share - select Pixelmator Photo (or open Pixelmator Photo and select the photo). I make some edits and click Done.

The thumbnail of the photo immediately reflects the edits and the photo is being uploaded to iCloud Drive. So far so good. I can see the photo in question being synced on my Windows PC.

However, a few seconds after the upload is finished, a download is triggered on the iPad for the just edited photo. Once that is done, the photo is corrupted: it loses all of the edits, has been rotated and is only partially visible (grey bars on one side of the photo). This is true for the copy on the Windows PC as well as the iPad. This happens every time.

I tried the same steps using Dropbox and did not notice any problems there so I assume the issue is with iCloud Drive.

The only way to avoid this with iCloud Drive appears to not have the photo locally available on the PC. However, that would be cumbersome.

Any help greatly appreciated.