Cannot add my Schlage Connect Lock to SmartThings Hub

Do you have any custom device handlers installed? If so remove them or republish them due to the stale DTH issue with unused DTH’s.
Ideally you should only be using one of two DTHs’ for the Schlage connect, the stock “Z-Wave Lock” or the “Enhanced Z-Wave Lock” DTH.
If there are any unused lock DTH’s lying around in the IDE it can interfere with the lock pairing process.