Hi Rui and thanks for jumping in here Frank ??
I’ve checked your site and for me, the popup shows up on the first load only, on the second one it will show the error that you mentioned above.
So it seems that it happens once the page is cached, however, I still can’t replicate this behavior on my site ??
I would like to get some recap on the current setup that you’re running based on the above discussion.
Superpwa – Is it deactivated completely now, can you perhaps try removing it so we can make sure it doesn’t have some leftovers still running on site?
Windscribe – It’s the VPN service, correct? That’s also disabled for you now, correct?
HTML, CSS and JS optimizations are all off now but the issue is still there?
Is W3TC still running on your site, did you try completely uninstalling it because W3TC is known for leftovers even after removing the plugin completely?
https://www.webnots.com/how-to-completely-delete-w3-total-cache-plugin/
Which WP version do you use and do you have JetPack running on your site?
Cheers,
Predrag