Hi Victor!
Thank you taking a look at our issue (and for hiding our site credentials from public :)). Yes, as my team reports, we have spent a while playing around with the issue. What was previously done:
1. Deactivating all plugins except EC
2. Switching to one of the basic long supported WP themes (2016)
But we are still at the same point. Also I have updated the WP version to the latest one.
Please let me know if anything else could be done from our side.
Regards,
Hugh