Welcome to the WPML support forum. My name is Nicolas and I will be happy to help you today.
Thank you for the videos. It helped a lot to understand the issue.
I tested myself and it seems that the exact same URL sometimes works and brings you the right filtered page and sometimes gives you a 404 - Page not found.
It seems that WordPress has a hard time to resolve those URLs. Let's try few WordPress related solutions before digging further:
1. Go to "Settings > Permalinks" and resave your permalinks
2. Review your htaccess file https://wordpress.org/documentation/article/htaccess/
3. Make sure that your category URLs don't create a conflict with an existing page with the same URL.
4. Make sure that all your slugs are translated correctly because for example:
- from the PL: hidden link
- I can use the language switcher and get SK: hidden link (oferta)
- But once in SK, if I click the link in the menu the url is: hidden link (ponuka)
Here it seems that the product category prefix is not the same. /ponuka is the product category prefix slug and /obytna-vystavba is the term slug
I will give you an access to WP admin panel, so you can check all slugs.
All products category prefix slugs are correct - hidden link (look at the screenshot).
All term slug are avialable here - hidden link
There shouldn't be such links as: hidden link or hidden link (oferta) because we have hidden link (ponuka) and hidden link (offer).
It's weird because once everything works fine on SK version and the next moment it doesn't.
Moreover within all other verions everything works good till we go to SK version. Then we have 404 error everywhere. Look at this video - hidden link
Sure, you can provide me with a temporary admin access (wp-admin and FTP) – preferably to a test site where the issue has been replicated – so I can further investigate. I will activate a private field for your next answer where you can provide that information safely (this field is only visible by you and the support team). Don't share your own admin account, create a new one that you will delete when we finish troubleshooting.
IMPORTANT: Before we proceed, please backup your site and database.
Then in "String Translation" I found that you translated that string in SK (see screenshot).
I think that's the issue here, so I deleted that string from "String Translation" and it seems to have solved the issue. I navigated through several categories, switched languages, cames back to SK and navigated again and I didn't get any 404. The only links I couldn't test were the ones on the homepage, those are still pointing to the production site urls (.eu) instead of the dev site.
Could you please check by yourself, and if the issue is resolved, do the same thing on your production site and let me know how it goes.
