In regard with SharePoint Online Alert:

With the old version – when you uploaded a document you automatically received the properties screen and could add all the applicable metadata before you officially checked-in the document. Once you did that, a single Alert was triggered for the user (if they were setup to receive alerts).

With the new version – when you upload a document you no longer get the properties screen and it appears an Alert is triggered by the upload. You then have to go find the document and add the applicable metadata which is then triggering another alert with those changes. So, at a minimum, users are now getting two alerts when they used to get one. To muddy the waters further, on the initial document upload, since there are no properties, the document is appearing in multiple “views”. If a user has an alert setup for several of those views, they will get several Alerts saying a document has been added. So, in some instances they may be getting 3+ alerts for the upload, and then another for the properties update.