Add new category doesn’t work

Hi,

We have been having problems with not being able to add new categories (either from the productpage or from the category page).

On a product page, it doesn’t show any error, but it just doesn’t work.
On the category page, it shows it’s busy and then you get an undefined error.

We have updated the theme, woocommerce, wordpress, we have disabled and enabled all of them, but the problem is still there.

Can anyone help me fix this? Thanks in advance!

Marielle