Mac only approves password on second entry
The reason you're asked to enter password two times may be because FileVault is enabled. When FileVault is enabled, you're first prompted to enter in your login information to unlock the disk at the EFI Login Window, and then you're prompted to enter in your login information again to go into your actual user account. 

Recommended workaround is


You turn off FileVault (System Preferences → Security &amp; Privacy → FileVault),  or 
To allow automatic login when FileVault is turned on, enter this on Terminal

sudo defaults delete /Library/Preferences/com.apple.loginwindow DisableFDEAutoLogin



Please refer to this Apple Support Communities thread for more details
https://discussions.apple.com/thread/7690125