Question Animation dont loop seamlessly

Hello, i'm stuck with a very basic hand made animation, my object simply rotate from Y = 0 to Y = 25 and next Y = -25
Basically rotate on right then left.
Loop Time option is tick on my Clip, start key and end key are set to auto in animation curves and the curve look pretty seamless now
My animation last 479 frames, beginning rotation is Y = 0 and end rotation is Y = -0.01
And yet, animation seem to slow down at the very end and that break the seamless flow
I can't figure why and it's a bit frustrating to not be able to deal with
Am i missing something important or doing something wrong with the animation setup ?
Thank you for your attention, and i hope someone will have a solution to solve my problem !

 

Do you have Loop Pose ticked?

Also, your curve looks a bit off at the start and end.

 

Loop pose was not ticked, but the issue is still occuring after i ticked it.
Start and End point of my curve are both at Y = 0



I finally switch my two curve controls point to Linear on both tangents and it see to loop seamlessly now


I'm still open if anyone have a solution to loop the animation seamlessly using the curve on my first post ?