"save and stay" product randomly not saving 1.6.0.11

[mrweb]

Hi

I need your help about a Prestashop 1.6.0.11

Sometimes, when I update a product with "save and stay", the page go to products list and it don't save the changes
Sometimes... its works

Nothing changed recently : no update, no new module

Did you get this bug too?

How to display the process of saving and find where is the bug ?

Sql databse with 2G
Php 7.0

Thanks for your help !