I think the right left leg looks a little weak and it does look like he is planting both back legs together instead of striding. However, he is a puppy and this is a just from looking at the videos.
It looks like overall he could use more muscle mass in his hind end. Do you do low impact exercise with him or is it all running and jumping? Rafi was like that when I adopted him at age 1.5. I built up his muscle, gave him supplements for his joints and don't let him overdo the high-impact exercise and he is doing great now at age 7.5.
Ruth & the 4 Legged Rescue Gang
Rafi the malaroo
Gio & Varda, the krazy kittens
....In my heart: