Hello, @Martine,
When I try to open your site to check and solve your issue it shows an error as you can see in this image: https://postimg.cc/WDQBJT2T so kindly check it and fix it so that I will be able to log in to the admin dashboard panel also, Please try to disable all the third-party plugins (including cache plugins), that does not come bundled with XStore https://xstore.helpscoutdocs.com/article/36-included-plugins, clear the cache of the browser, and check then. Maybe one of the additional plugins is the reason for the problem.
And if the issue will still persist then please remain all the third-party plugins deactivated on your site and allow permission to debug your site which includes deactivating all the third-party plugins and on-site Customization as well so that I will check and assist you accordingly.
Note: Please take the complete backup of your site first.
Regards 8Themes Team.