cant save prices to prestashop multisite all shops

[moatazattia]

Describe the bug
when i try to save product price while setting on All shops mode , price is not saves, but when i save it on single shop its saved ok... but not in all shops..
its major because we cnt make global changes on product except from multishop

moreover , when save the product to another shop and try to change settings it affects all shops..

which means i have to upload same product everytime shop by shop

it happened suddenly , before it was okay..

i have prestashop multisite 1.6.20

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Catalog , Products , Price in ALL SHOPS mode '
2. Click on 'save in multishop mode'
3. Scroll down to 'top page'
4. See error zero price set

Screenshots
attached

Additionnal information
PrestaShop version: 1.6.20 multi shop , multi currencies , multi languages
PHP version: 7.2

Edited November 24, 2018 by moatazattia
adding image (see edit history)