Facebook group reach zero

I have 4 groups.
2 off them have 500 000 members.
Until the 7 august the posts gets likes and shares.
8 august the groups with 500 000 is dead.
I upload photo and videos and nothing. Then I upload the same content to other groups and iget likes and comments
My other groups works great

Same with pages !:

You are not alone:
https://www.blackhatworld.com/seo/facebook-page-zero-reach.956122/