I have same issue here. and t-p, I already try your suggestion and faced these problems.
First, via phpMyAdmin, I can’t found the line active_plugin in wp_option table which is written in that Instruction you’d linked. So I can’t deactivated plugin via phpMyAdmin
Second, deactivated plugin via FTP, I also try to follow the instruction in that link. But nothing changed too.
Finnaly, I upload fresh download excpet wp-config.php and wp-content and nothing change. But thanks anyway.