I discovered that when my character (a bird) flies at a certain position, it gets stuck and can’t move, because it collides with terrain (the terrain has the name ‘island’).
Why is this happening?
can you take a picture were the bird object is selected so that we can see the collider
Yes. It is a sphere collider.
The bird seems very low… if it has its wings upward, your sphere collider may collide with the terrain on the first screenshot.
Play your game, pause it (do not stop it!) and look in the scene view what exactly is colliding
The scene was paused - the bird is in the air, it’s just not shown in the picture. Here is a clearer one.
have you tried to remove the collider or to make it smaller?