Too much change at once.
Do the Alexa migration first or Classic to New first and wait until you’re COMPLETELY Done before trying the other. Don’t do both at once.
Because the Alexa deadline is sooner do that one.
- go into Alexa and disconnect the SmartThings Classic skill
- go to alexa.amazon.com, and delete all devices and scenes connected to Alexa
- have a cup f coffee. You don’t need to wait an hour but a few minutes do help let everything get settled.
- Log back into Alexa and Connect the (new) SmartThings skill
- Discover devices
- Fix everything that’s broken. (Put devices in rooms, fix routiones, scenes, etc.)
Wait a few days and let this stabilize before moving to NewApp