[Resuelto] Translated slugs lead to 404 error

I have an issue on my main website bulgarimot.bg but the problem is also the same on my staging version which runs with bare minimum plugin:

Please use the staging version which has the exact same issue:

enlace oculto

When accessing the English version:

enlace oculto

It's a 404 error (Back to homepage).

The working page : enlace oculto

Should be enlace oculto ... as WPML understand it correctly.