Add to cart not working with activated GTM for WP

Hello there!

I just updated my WooCommerce and WooCommerce Germanized to versions 3.9 and 3.1.1
Now the add to cart process doesnt work anymore for simple product pages when GTM is activated.

We are also using WooCommerce product addons (latest version) on out simple products.

Any idea why this is happening?

When clicking add to cart the page simply reloads, but nothing happes. Seems like a javascript conflict to me, but I can not see anything in browser console.

When adding products to cart from our custom templates things work fine. (event pages).

Only simple products are affected.

thanks for looking into this.