There will be others who have a different opinion that I do, but I will NEVER NEVER lope a barrel pattern on grass. NEVER.
I was simply slow loping
my horse in this video freeze frame and look at how much he needed to dig into the dirt.
Grass is slippery and grass does not give your horse ANY traction whatsoever. They have nothing to dig into.
Anyway, that's my soapbox for that. Video from January
You have no bend in your barrel turns. He body is straight.
You need to help him more. In order for a horse to turn a barrel properly, they need to be bent in a circle, from nose to tail. Like this:
Also, when you left the 3rd barrel, your horse was on the wrong lead. The video is too blurry to tell what happened during the turn. It could be that he is not using his body correctly, so his feet got messed up. Or it could be the ground you are asking him to lope on (grass.....). Or he could be sore somewhere. Usually that's when horses will swap leads, or be on the wrong lead in a turn.
Right now, your pattern looks like you are just happening to be turning 3 times around 3 cans. It doesn't mean like your horse is connecting what he is supposed to be doing. April Video
I'm guessing your horse broke stride around the first barrel due to poor ground and due to no bend in his body (and not using it properly).
You ride nice and quiet. But use your body and your legs to cue him. Your inside leg should be pressing his ribcage outward, while your outside leg keeps his hip inward and underneath him. Use legs, legs, legs, and get him using his body correctly.
I would read over this barrel sticky if I were you. Lots of great info in it. Barrel Racing Exercises and Drills.