Thanks everyone. I still can not reproduce the locally, but the linked website helped. It seems related to a change in our JavaScript bundler combined with running “optimization” plugins that combine several scripts into one.
We recommend excluding the Koko Analytics script from such optimization, as it is very bug-prone and not necessary now that HTTP/2 is a thing. The full path to the script to exclude is as follows:
/wp-content/plugins/assets/dist/js/script.js
In the meantime I’ll try and see if there’s anything we can do from inside the plugin to prevent the issue from occurring.