Selecting all plugins or all products doesn't work anymore

Ik gebruik WordPress 4.5.2 + Woocommerce 2.5.5, met the latest Divi theme from Elegant Themes. I have several plugins installed with it.

In Woocommerce I am selling variable products only. When I wanted to update the stock of my products there is an option to extract all variables of each product, so I can fill in the amout of stock and save it. But after some updates the setup has probably changed and the menu of the products also looks different then before. That is nog much of a problem; it needs to look like that and it is jusit simply the new look of it.

But when I go to Products –> Select one of my variable products to edit it –> Scroll down to: ‘Amout in stock’ and fill in the amount of stock I have, and then try to save the news setting, then the cursor jumps to the beginning of the page (top) and nothing happens. No variables of any product are extracted. Also: when I try to select all products at once, only one selection box is checked but not all the plugins.

This also happens when I scroll down to the option where I can extract all variables. Nothing happens, no variables of any product is extracted.

The second thing I noticed: when I go to the Plugins page it should be possible to select all plugins with the upper selection box. But when I select that box only that box is selected and none of the plugins.

I checked these both option (product editing and selecting products and plugins) and on the same pc, with the same browser and same hosting packaged these problems do not exist. All sites are seperatly installed with a single WordPress installation per site.

What I already tried:
– Update all
– Deactivated all plugins; problems still there
– Removed the Divi plugin by selecting the TwentyFifteen theme, removed the Divi directory, uploaded the theme folder again and activated it again; problems still there
– Deactivated the Woocommerce plugin, removed it, reinstalled it and activated it again; problems still there
– Downloaded the core files of WordPress 4.5.2 and uploaded by FTP, ACCEPT the ‘wp_content’ folder; I left that the same, and I didn’t uploaded the root-files, like index.php etc. After this all: the problems are still there

So, is anyone familiar with these problems?
Are they connected to eachother?
Does anyone has any idea how to troubleshoot this any further or solve this problem in any way?

Thanks a lot in advance!

Best regards,
DM