Trying to get property of non-object in i18n_langcode() (line 229 of i18n.module) and a bunch of other property of non-object notices
Finally solved this mystery. 

I was able to narrow it down to a bean block in the site's footer. Upon inspecting all of the bean's block display fields



Disabling this field fixed the issue. Where is it coming from? IDK yet. I will update once I know. Seems like custom module. 

Update

Yep, turns out Featurette image link is coming from a custom module. Notice the big error in line 24 and line 30.



More errors here, what a mess!