Try a few things:
- Exclude the lock
- Remove the Alexa integration
- Delete all your existing SmartThings devices from the native Alexa app
- Pair the lock with the hub
- Connect Alexa to SmartThings
You may also want to look at this topic which may help if you’re experiencing performance issues: FAQ: why would I need another beaming repeater if my zwave lock is already close to my hub?
In addition the Schalge Connect BE449 has a firmware bug which causes missed notifications, this device handler can help fix that issue: [RELEASE] Universal Enhanced Z-Wave Lock Device Handler for Schlage, Yale, Kwikset, IDLock, Popp, Danalock, August Pro, Keywe, Philia, Samsung