Background of the issue:
With a Dutch website super-seat.com, there is a German version on super-stuhl.de. Both websites are under the same WordPress installment on super-seat.com and it is configured with WPML to use the website with two languages. This site uses the plugin Custom 404 Pro from Kunal Nagar to have a page selected as the 404 page.
Symptoms:
When I select a 404 page for the Dutch site and after that one for the German site, the Dutch 404 page selection is removed and vice versa. So this plugin is not WPML compatible.
Questions:
Do you have any other plugin you recommend for a custom 404 page selection which is compatible with WPML?