If the folders were created in Outlook, they might not have synced back to the email server. I suggest logging into your web-based email to see if they are available. If not, I suggest checking your Outlook to see if they are still listed there.
I just had to manually recreate all folders in web view sync and copy content back into them. Why will workspace not sync when folders are created in outlook 2016.
Also note that the fact my online and off line folders were different was leading to delays highly variable in delivery of incoming mail to my outlook inbox. That is now solved but I woudl like to find out why when I create or modify a folder in outlook2016 that is not sync'd to the web view and obviously the server view.