What’s a language where the textbook version feels completely disconnected from real life speech?

Some languages feel manageable in lessons, then you hear natives talking casually and it suddenly feels like a different language entirely. Words get shortened, grammar changes, people mumble, or whole phrases disappear.

I am not really talking about obvious cases people always mention. A more interesting one for me is European Portuguese. The textbook pronunciation feels very clear, then real conversations start sounding way more compressed and fast than learners expect.

What language felt like that for you? One where the “study version” and the real spoken version barely felt connected?