Going behind can be explained by the AI not being able to reach it’s destination, therefore does a little circle around it. Yes, it should also be able to reach going straight if it can by going around it but because it foresees that it cannot, it starts traversing around while getting closer and at some point it passes the nav mesh bound due to it keeping it’s existing velocity, making it reach the acceptable radius. This can be fixed by either decreasing the cell size from the details window that opens when your recast nav mesh is selected, or increasing the acceptable radius of your Move To Actor function.
About the off movement at the start, the only thing I can think of is the pathfinding algorithm detecting a shorter path and doing a little detour. It seems illogical upon observing your GIF, but maybe there’s something we’re missing. Maybe try placing the AI on different parts of the map.
To provide some guidance on your debugging process, you can project it’s navigation via the function to get some clues on what’s happening (also open the AI debugger during runtime), you can try using the Move To Location function instead and plug the target actor’s location into the destination pin, and you can try doing this exact experiment in a completely flat surface.
Hope these can be helpful 