Hey @matthias-wagnerfalkemedia-at,
You are right that this is a WooCommerce conflict. They install a different version of select2 called selectWoo, and it has an issue with rendering templates: https://github.com/woocommerce/selectWoo/issues/39
We’ve got a workaround in testing right now though, and we should have a patch out for this shortly! I’ll let you know once it’s available.