The new Page message generating 404 on Facebook

On Facebook, I like a few pages and I subscribe to notifications of new posts from these pages.

So, whenever a page generates a new message, I receive a notification.

These lead me to a URL like https://www.facebook.com/pg/page-url/posts/?ref=notif

for example. https://www.facebook.com/pg/happysmartspage/posts/?ref=notif

Since one month, they produce errors of:

Sorry, this content is not available at this time.
The link you have taken may have expired or the page may only be visible to an audience you are not in.

If I change the URL to https://www.facebook.com/pg/happysmartspage/ I will see the new message at the top of the page.

It seems so that the https://www.facebook.com/pg/page-url/posts/ does not work for me.

Help appreciated.