In case of AFS, why do unrealized gains/losses go to OCI but in case of trading, it goes to PnL?
Because those are the (arbitrary) rules of accounting.
No logic, is it?
None of which I’m aware.
That’s the biggest problem with FRA: you have to memorize a (large) number of arbitrary rules.
Under US GAAP, interest expense is a non-operating expense, but interest paid is a CF O outflow. It makes no sense, and you have to know it.