Backups not working from WordPress

I’ve using simple backup plugin for about 6 months, and it worked just fine, until today that it said it created a backup, but actually didn’t, installed xcloner plugin and had the same problem.

So checked the backup folder permissions, it’s on 755.

It looks like that the functions:

mysqldump --single-transaction -u
and
zip -r

aren’t working, but I don’t get any error though, nothing like that, I actually get a successful operation.