Sometimes both Mac and iPad are online. My question is in this situation if I change the note in one of iDevices, will iCloud syncing be confused between the two iDevices? In some note taking apps such as Notability , I’ve seen this confliction that finally duplicated notes was the result. iCloud confused to select the note of which iDevices. I wrote one note in ipad , but Notabilty created duplicated notes in iDevices.
You should be able to edit on two devices at once no problem. If you edit the same line of text on each, at the same time, you may end up with something different to what you wanted. But you should never see duplication of notes or paragraphs. We do our best to merge things together in a logical way.
Then it is a fault of the app, not iCloud. Is it true?
Sync is hard, so easy to dismiss, but in general, yes, it’s the task of the app maker to account for possible duplicate creation, merging, etc.
As @mekentosj mentioned, it is down to the app maker how they go about merging conflicts that arise from you editing on two devices. Note that the duplicate data some apps make may be a conscious decision on their part. A lot of apps will choose to simply give you both copies when there is a conflict, and let you decide what to do, rather than try to merge things together. So it is not necessarily a bug, but can be a conservative decision to let the customer choose what to do.