Mostly were not misconceptions but actual ignorance.

But if I really had to pick one, I'd say anatomy study. In Antiquity, Greeks statues got to a point where anatomy was reproduced way too accurately (See Lacoon in the Vatican). This could've only been the result of attentive dissection studies, flaying or skinning.

The church never allowed this until Artists of the caliber of Leonardo/Michelangelo needed it to improve their commissions.

Giotto, Michelangelo all lived in a time where Roman/Greek Ruins were being rediscovered.

Petrarca (Italian poet) looking at the old Roman sites was stunned at how backwards we got during medieval times.

I put most of this due to Church State, they had the monopoly of information and education.

And so there you have it, greeks were dissecting, we forgot about it, we came back at it in renaissance and later with Vesalius publishing the first Anatomy Atlas.

Hope that answered your question, if not in full at least partially 🤗