Modern Auth enabled, user outlook prompt password but not able to authenticate

Dear All, 

We enable Oauth for our exchange 2019, once it is done, we started to see user keep prompt for password. once upn and password enter it does not takes in. showing outlook unable to connect to server with below error 

not sure what was the issue, but we disable oauth, issue will certainly gone. this only happen to small portion of people not all user affected.