Hi
I’ve had the same issue with a few sites I manage and have found a way to fix it.
I’m no expert so backup your files if you’re going to try this.
All I did to fix this was replace misc.php located in wp-admin/includes/misc.php with the previous version of the file. I could then log in to the dashboard and update wordpress manually without problem.
Can’t attach the file but am sure you will be able to download the older version of the wordpress website I used the file from 4.3.1
