The crux is that SSH even when connecting w/ -vvv or -vT modes won’t tell you precisely why it’s not connecting for obvious security purposes. This is presuming you’ve double checked all other obvious issues and your public/private key pairs are setup correctly.
In the linked post above Kent Martin writes, the answer is to bind debug to an alternate port on the server side:
/usr/sbin/sshd -d -p 2222
then similarly from the client machine:
ssh -v -p 2222 user@machine_I_am_trying_to_ssh_to
On the server machine terminal you’ll see a more verbose debug log and hopefully it will tell you exactly why your client machine is being rejected.