Dear timo,
Thank you for the response!
did not create any tags or tasks on the ipad, the app there was empty.
All the data was on the iphone.
However, I did switch on the sync on the ipad first, and then on the iphone, which must have then caused the overwrite with the empty data. However, it seems to me to be a very easy issue to check and prevent, e.g. by raising a warning “you have db conflict, do you want to continue?”, or even “which db do you want to keep - ours or theirs?”.