user is unable to log in in Production. Always getting redirected to sandbox account

@vishalthoughts is probably correct. Either

1) the user never got assigned a role in production

2) their email is different is sandbox/production (and thus is an entirely separate account/login)

3) they last logged into sandbox, and thus are being automatically logged into sandbox, and don’t understand how to switch accounts/role via the dropdown in the top right

4) they are being offered the option upon login to select roles and don’t understand how to select the correct one

If none of those, then you’ve really got something weird going on, and will have to contact support. But most likely scenario is an issue on the employee record or lack of user training/knowledge.