You are using a Gmail account for emails in Kennel Connection and it suddenly stops working or you are entering the settings and testing for the first time. The error shown in the email log displayed is "Failed to get response to login password" but the password entered is correct.
Gmail has added an extra security option in their account settings that disables third party apps from connecting to your account.
The new security option needs to be set to Enabled in order for KC to connect.
In this screen shot below, you can see the security option on the left that you must click to get to the "Less secure app access" and the "Less secure app access" section. In this image, it shows that the option is already set to ON so this is all set.
Your changes will be saved automatically and you should now be able to connect through Kennel Connection
NOTE: You cannot use 2-step verification if you want to use third party software like KC to connect to your email server.