I have 5 languages and all my fields are translated into them. My default language is ancient Aryan.
When I clear cache English translations of Fields Labels are displaying in default language. Other languages rest ok.
When I change English translations of fields labels nothing changes.
Only when I rename one of field labels on default language all English translations of field labels become ok.
What to do if i like to clear cache?
I described bug here: https://www.drupal.org/node/2790131#comment-11574329