finally I fixed the problem, the Warning is just a warning, not the actual error.
I managed to get to the bottom by “selecting the error” and then Ctrl+c and paste it to your favorit Notepad/++ (ctrl+v)
Inside Notepad, I was able to see the whole error messages. The message comes after all the warning messages being printed. For me, it was an undefined variable in custom-variables.scss because I was migrating theme from Atlas2 to Atlas3, somehow I was still using the old file, and there are several new variables that are used in Atlas3 but were not exists in custom-variables from Atlas2.