InnoDB tables deleted

Hello.
Using MariaDB for a few months without any problem, last Thursday all tables except one disappeared from one of the databases.
I didn't have binary log active. (sad, I know)
Trying to repair the tables didn’t work with error that the tables don’t exist.
Trying to innodb_force_recover until 6 (all tables are in innodb format), the system recovered two other tables, but without data.

From the logs I’m almost sure there was no hacking attack and I’m sure I don’t have any drop command from any application, and I also check HeidiSQL logs for any command like a drop or something that could do this and I didn’t found nothing.
I recovered most of the data from last backup and some data from my application logs, and in the next morning the plant could restart the production. (one problem during restore is the disable keys command doesn’t work on innodb tables and so some data was not restored)

Now I need your tips/help for the following:

• I need to explain to the client and to my boss what occurred. (using mySQL for 2 decades never had nothing like this). There is any issue that can affect this version? What log files should I check?
• I need to take some measures to ensure that it will not happen again in the future. Any advice?
  Thank you.
  Nuno Ventura