A couple things to check if you this type of error.
The error is given by the client. So check your client know_hosts file.
For additional debugging try connecting to the host using verbose mode.
i.e.
ssh user@hostname.com -v
https://dan.langille.org/2013/06/11/sshd-error-key_read-uudecode-failed/
https://www.chrisnewland.com/solved-ssh-sshd-error-keyread-uudecode-267
https://rlaanemets.com/post/show/git-and-ssh-key_read-uudecode-xxx-failed