Intro to Animation: Down Pose

I animated this using the image alone instead of the video, just to see if I could manage it without painstakingly emulating everything in the tutorial. Everything looks fine in the 25 frames I animated myself, but as soon as the cycle takes over, the left leg begins to straighten, starting on the 38th frame and constantly repeating. I spent ages trying to figure out why, but I'm still not 100% sure what could be wrong.

Intro to Animation: Walk Cycle Mechanics

Intro to Animation: Paper Clip Chain

Intro to Animation: Felix Jr.- Rig Installation

Intro to Animation: Rotating Bouncing Ball

Intro to Animation: Bowling Ball

Intro to Animation: Bouncing Ball Non-Centred