Drupal 8 – Site language changing abruptly

I have a Drupal 8 site with version 8.2.3. I have two languages configured on the site.
Default – English and other one Spanish. Issue is site content is getting translated randomly. Spanish content is seen on the site when the current language is English and vice-versa.
After rebuilding cache (Drupal cache as well as serve cache) , it works fine.
I didn’t get any way to reproduce this. Translations changes randomly and it affect different entries every time it happens.

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/30/feed