First of all, I'm not a get up technician. I was RKC certified and recertified over a decade ago when Pavel was there and have taught a number of people here and there over the years, but besides demonstration reps, I've barely practiced or trained the get up . It's just not my thing. So any real get up aficionados, feel free to correct me.
But I notice a couple of things that might be causing discomfort.
First, if your elbow hyperextends, work on finding and maintaining a neutral position. If your elbow tends to go beyond neutral to lock out, learn what neutral feels like, stop there, and don't go all the way to the end of the range of motion.
Second, maybe it's the camera angle, but it looks like your tall sit is not as tall as it could be. Since you are not sitting tall, you need to put more pressure on your arm to support your upper body and the bell, and your shoulder ends up very extended with your hand quite far behind you. If you start with your support arm at about a 45 degree angle to your torso, your hand ends up about even with your hip, not way back behind you. On the way down it should be the same.
There may be some mobility/flexibility issues restricting your tall sit with the bell overhead (very common), or it may just be a matter of paying attention to it.
I totally agree with this, but just from that picture, I feel like being able to sit up tall and support the weight through your torso to your hips instead of taking a lot of it on your down arm might make a big positive difference.
Here's a StrongFirst video of Zar Horton demonstrating a get up. Notice that on the way up, when he reaches the tall sit, he slides his hand in closer to his hip because he is sitting up very tall. He doesn't do this on the way down; he just puts his hand on the ground and keeps it in one position until he is all the way down, but the point is that the taller you are sitting, the more vertical the down arm is, the closer the down hand can be to the hips, and the less pressure is on it in the tall sit.