Can't Get New Smartthings Hub to add devices with Classic App

[TonyFleisher]

Sounds like you may have 2 locations and the classic app is defaulting to one without a hub.
This post has some details that may help:

FAQ: Common issues encountered migrating from a SmartThings to Samsung account (or: "Help! My hub/devices have disappeared!")

The issues The following are some issues experienced by users after migrating from a SmartThings account to Samsung account or by users who have previously added Samsung Appliances and TVs to the Samsung app/account before they had migrated their SmartThings account. Note: Samsung can implement this migration without you realizing it. They don’t send a notification before or after the actual migration event. Devices are missing in the Classic app. Hub/Devices are missing in the Classic app and you are prompted for the Welcome Code to add the hub. Devices do not appear when you login to the SmartThings (Samsung Connect) app (STSC). Two duplicate locations in IDE and unable to delete the empty one. Hub and most devices are in one Home Location and Samsung Appliances and TVs are in another…