If you’re still having issues, sometimes the setup gets corrupted and you have to run a special removal tool to get rid of it discussed here - Can't Remove Home Assistant smartapp
I know you said you completely redid the server, but if you restored a home assistant backup, the corruption will just come over from the backup. Basically the way this integration works is that it creates a smartapp within home assistant that communicates with the Smartthings API. API’s are just interfaces and don’t really run anything, and just respond to whatever the commands coming into it are from where the app is actually running.
Removal tool: