It kind of surprises me that people working in that environment haven't been better trained about what not to write. I have zero legal background, but even twenty years ago at my very first corporate job I received a training module about legal discovery and the consequences of poorly worded emails -- and that was at a company that I genuinely believe was trying to follow the law in good faith, and was simply worried about liability due to misperception of careless language.
For a team specifically working on a legal compliance project, I am with the poster above that mentioned legal teams providing oversite. If nothing else, every one of these chats should have had a lawyer logged in to provide a mental reminder to participants that the conversation really isn't private.