Icing is a huge concern. On a drone it just adds weight but it can add up.
Don't fly through clouds.
Flying near waterfalls is where you could find freezing mist. That can accumulate very fast.
Agree with Cafguy, a shinny surface probably confuses the downward sensor. Sorry I’m old fashioned, I always use a folding landing pad, 1. To provide a clear source for the downward sensor to pickup on and 2. To prevent any dirt from being blown...