[Resolved] Content automatically translated back into source language

Background of the issue:
Hi, we have a multilanguage website with English as default language. We have noticed that several pages previously translated into Spanish now have some content automatically translated back into English.

Symptoms:
Content automatically translated back into source language

Questions:
Why are some pages previously translated into Spanish now showing content automatically translated back into English?
How can we prevent content from being automatically translated back into the source language?