Can’t edit any post

I am unable to edit any published post. After editing as soon as I hit the ‘Update’ option it keeps telling me ‘The response is not a valid JSON response’.

Now, I did some readings in this topic. And as suggested in those topics I tried to ‘save changes’ of permalinks settings. But as soon as I hit the ‘save changes option’ the screen freezes into a white screen. Don’t know how to resolve it.

I am using only one theme and one plugin (twenty sixteen & all in one seo pack). I don’t keep unnecessary or less important stuff on live site. And my current permalink settings is like this /post_name/post_id

Any help is much appreciated!!