When the db with edited or deleted statement as mentioned above went through without error message, I see there seem to double entries.
The newly, automatically created db had empty zenkg_products, zenkg_customers etc.
Then below those another section continues with znc_products, znc_customers etc, which are the real stuff.

Perhaps the website tries to show zenkg_products, which are empty, I guess.
I am not sure the way I edited the db is right or not.
These may shed some light.