I had the same problem when I updated the mysql server from 5.5 to 5.7 in Debian 8 (jessie). In rare cases, it probably happens if you update directly bypassing the sequences of versions. (Many people do this, but such upgrades are not officially supported).
In my case, it worked fine when I executed the command below:
mysql_upgrade --force -uroot -p
I hope this will help you