OneDrive - User disabled and re-enabled.

Hi.. As far as i know this depends on the retention period you have set for orphaned onedrive for business sites.

Ideally, when you disable a user, (assuming on your local AD you change the OU membership to an OU that isnt currently syncing to o365), the change is replicated to AZURE ad and this marks the users site for deletion. 

Depending on the retention period that you have, when you recreate the user, this time the users PUID is different. It notices that it has a site that is already existing and so appends a "1" and creates a new one.

From my experience, if you delete the user, and the timer job kicks in to clean up the user profile(30 days by default), but you recreate the user before the site is deleted that is when the "1" is added.

https://support.microsoft.com/en-us/help/3042522/onedrive-for-business-retention-and-deletion