I am on a switch so I cant attach screenshots but I will explane the bug below.

The bug is mobs chickens and cows mostly try and force themselves to path find outside then pen when the fence gate is closed.

My guess is when the gate is open they path find a space outside the pen but if you close the gate first they infinity try to walk into the closed gate 

Steps to reproduce. 

1. Make a square pen with only fences and 1 fence gate
2. Spawn some mobs like cows or sheep
3. Open the gate and wait for a mob to try and walk out
4. Close the gate before it makes it out unless it tried to move somewhere NEAR the gate but still inside the pen it will forever stick its face into the fence gate unless you open the gate{}

Expected result: The mobs stops path finding outside the pen when it is obstructed **

Observed result: The mob keeps trying to escape the pen until you open the gate or use seeds or potato's to lure it (dependant on the mob)